The Antichrist of Silicon Valley has been in London this week.

At least, that's the title that Andrew Keen, a strident critic of web utopianism, revels in. Mr Keen is a British-born entrepreneur who made his fortune in Silicon Valley and then decided, with all the zeal of a reformed smoker or lapsed Catholic, that everything the web 2.0 evangelists stood for was evil. What really gets his goat is the idea that the web liberates everyone to become a journalist, film-maker, musician - or encyclopedia author - thereby devaluing the work of professionals.

His book The Cult Of The Amateur is an enjoyable rant against web orthodoxy which sometimes descends into bathos as he describes how seasoned professionals are being put out of work by amateurs with a YouTube account or a penchant for editing Wikipedia entries. It would take a heart of stone, for instance, not to weep for the advertising professionals whose careers he sees threatened by kids making viral ads with a handycam and sticking them on YouTube.

At a dinner in London, Andrew Keen challenged an assembly of web worthies - entrepreneurs, thinkers, even a few grubby technology journalists - to explain why they were so enamoured of the amateurs. Why, he wanted to know, was there such reverence for the citizen journalists and bloggers and musicians who were eating our lunch? He seemed particularly offended by Wikipedia, expressing incredulity at the idea that the whole project depended on people who worked for nothing.

But whether or not you agree with Mr Keen's analysis that "Web 2.0" is a threat to our culture, his analysis is now beginning to look a little dated. Amateur hour on the web may be drawing to a close. True, new technology is lowering the barrier to entry in all sorts of professions. In my own business, journalism, it's never been easier or cheaper to write, record and film reports for the world to share.

But what is now becoming clear is that it's much harder for amateurs to get an audience. Who, for instance, are the most successful bloggers? Well, many of them are actually old-fashioned professional journalists working for mainstream media organisations which pay them to blog.

And whatever we were told a couple of years back about unsigned bands making it big on MySpace and new film-makers breaking into the big time on YouTube, I've yet to spot the new band or movie which has made a major impact without the help of a record label or a studio. The professionals have woken up to the power of Web 2.0 - and are moving in to colonise it.

There was a long discussion at the dinner with Andrew Keen about the difference between an amateur and a professional, but to me it seems pretty obvious - professionals get paid, amateurs do it for love.

That's not to say that people in all walks of life - writers, musicians, politicians, perhaps even bankers - don't start off driven by creative or idealistic passions rather than by the need to make a living. But many of the amateurs will either fade away, discouraged by their failure to command an audience, or will turn professional.

Certainly, many of the Web 2.0 companies - from Facebook to YouTube to Twitter - seemingly started off with hardly a thought as to how they might profit from their activities. Now harsh economic times are forcing them to look down at the bottom line rather than up at the stars.

Andrew Keen may be right that we have an excessively romantic view of the amateur. But he shouldn't worry too much. His success is proof that there is still a good living to be made as a professional writer and provocateur.