A few months ago Bill Gates let slip an interesting thought about Google in an interview. It reminded him, he said, of Microsoft in its honeymoon period - ie. the decade 1985-95. This is the first time in recorded history that Gates has dignified a competitor by actually naming it in public: generally, he speaks only in paranoid generalities. But the Microsoft chairman knows trouble when he sees it, and Google does indeed pose a long-term threat to his profitable monopoly.
That's par for the course in the capitalist jungle. A more important question is whether Google spells trouble for the rest of us in the long run. And the answer to that could well be yes.

To understand why, we need to look back. It may be hard to credit it now, but Microsoft was once a cheeky start-up, run by college dropouts with long hair and a penchant for fast cars. It was founded at a time when the fledgling personal computer business was a labyrinth of incompatible hardware and software systems. In 1981, IBM effectively defined a de-facto hardware standard; and its erstwhile partner Microsoft defined the software standard by providing the operating system for the new, accountant-friendly IBM PC. Thus was order brought to an unruly industry. And thus was the foundation laid of Microsoft's subsequent prosperity - and its monopoly on desktop software.

We all know the rest of the story. Microsoft has grown and grown, to the point where its monopoly lock on desktop software makes it impossible for an upstart to supplant it: the world's organisations are so locked into the Microsoft Way that they cannot contemplate moving to a different operating system, even if it is cheaper or technically superior.

Yet, strangely, it would be wrong to conclude from this that Microsoft's position is unassailable. Granted, it has a stranglehold on the PC platform, and anyone who tries to compete on that territory is doomed to lose. The significance of Google's challenge is that it hasn't chosen to fight on that ground. Instead, it seeks to make the platform irrelevant.

And it's doing it. Here's an illustration. Ask any random audience of computer users the following questions. Who uses Microsoft software? (All hands go up.) Who uses open source software? (No hands.) Who uses Google? (All hands go up). 'Well', you say, 'that's a funny thing because you're all users of open source software: Google runs on Linux.' After the rueful laughter has died away, ponder on what that means. People want a particular computing service (in this case search), and don't really care what platform it's delivered on.

Since its inception in 1999, Google has focused almost exclusively on providing services that are platform-independent in this way. Its search engine can be accessed from any browser. Ditto Google Groups, Google Images, Google News, Froogle, Blogger, Google Mail, Google Talk and Google Maps. A few of its offerings (notably Google Earth, Desktop Search and Picasa, a neat program for handling and organising digital photographs) are written specifically to run under Microsoft Windows, but the most heavily used services are all independent of operating systems and hardware. The company has taken Scott McNealy's aphorism - 'the network is the computer' - and turned it into reality.

All of which is bad news for Mr Gates, whose prosperity is based on the proposition that the platform is the computer. But is it good news for the rest of us? Google's most intensively used services are accessed via the net, so all the data involved flows through Google's servers. And since these data are often fragments of intensely personal information - email, web clickstreams, instant messages, VoIP conversations - a single company is in a position to know more about each one of us than anyone would have thought possible even a decade ago.

Consider Gmail, Google's web-mail service. This provides two gigabytes of storage to each subscriber - enough to ensure that you never again have to delete a message. The flipside is that your messages reside forever on a Google server. What's more, Gmail is free because it is funded by advertising: Google's software scans every email, identifies key phrases, and puts what it regards as relevant ads on the right-hand side of the screen.

If you think that's creepy, you're right. Google's response is that the messages aren't actually 'read', that it's just a process akin to the one in which email messages are scanned by spam-blocking software. But that's disingenuous, because the ads selected for display are logged (they have to be, so that advertisers can be billed) and those logs will inevitably reveal something of the context, if not the content, of the scanned messages. Anyone who uses Gmail is therefore sacrificing a degree of privacy compared with someone who uses a conventional email service. That's why privacy and civil liberties groups have attacked Gmail on the grounds that it violates the trust of email service users - in particular non-Gmail users who send messages to Gmail subscribers. They point out that scanning creates lower expectations of privacy in the email medium and so establishes a potentially dangerous precedent.

Google's apparently unstoppable momentum is beginning to raise alarm bells across an industry that hitherto admired the company's cheeky, upstart ethos and the brilliance of its technology. This, after all, was an outfit that declared in its prospectus that its motto would be 'Don't do evil'. The implicit message from the co-founders, Larry Page and Sergey Brin, was: 'We're basically good guys. You can trust us.' But that was then, and this is now, when Google has evolved into a multi-billion dollar corporation with aspirations to global domination. Its corporate mission, remember, is 'to organise the world's information and make it universally accessible and useful'. And when these guys say 'world', they mean it.

So there's a strong possibility that Google will indeed turn out to be Bill Gates's worst nightmare, transforming his grip on the PC platform into a wasting asset. But the corollary of that is a world in which millions - perhaps billions - of people will become users of Google services, and that the company will become custodians of their most intimate data. The day will come when Google knows more about each of us than we realise. And knowledge is power.

Should we trust a US corporation with it? You only have to ask the question to know the answer.

Ten things you didn't know about Google

1 It's a calculator. Type '25 miles in kilometres' (without the quotes) into the search box and see what happens.

2 It can be manipulated to produce desired results. Try typing 'miserable failure' (without the quotes) and see what happens. This is called Googlebombing.

3 Googlewhacking is a game where you have to think of a single word which, when typed into the search box, will produce just a single 'hit'.

4 How many pages does Google index? Answer: nobody knows. Google used to publish a number under the search box (when last seen it was over 8 billion) but it has stopped doing that - possibly because Yahoo is now claiming to index 20 billion pages.

5 It does really useful online maps of the UK. Go to maps.google.co.uk. And you can search for restaurants, churches, bars or schools just by typing the appropriate term (e.g. 'restaurants in Bedford') in the search box.

6 Google's two co-founders are each worth about $7 billion. They are just 32 years old.

7 If you use Google's webmail, the messages reside forever on a Google server.

8 Google's power means that it knows more about each of us than any other internet search engine.

9 Google's Gmail software scans every email, identifies key phrases, and puts what it regards as relevant ads on the right-hand side of the screen.

10 Its services, such as Google Images, Google News, Froogle, Blogger, Google Mail and Google Maps can be accessed from any browser.