Haven't we been here before? America's technology-laden Nasdaq index doubles in the space of months. On both sides of the Atlantic, big-value flotations - Google, Virgin Mobile, Eircom - are announced or strongly rumoured for the summer. And all just four years after the catastrophic collapse of technology stocks. Are we about to witness another cyber bubble?

To find out, we naturally turned first to Martha Lane Fox, co-founder of Lastminute.com. But Britain's 'Queen of the Dotcoms' recently left the online travel agency and was uncharacteristically reticent: 'I have purposefully stepped out of everything for six weeks now, so I don't think I'm the person to comment.'

If Lane Fox is feeling fatigued, few could blame her. New media shares fell off a cliff just after Lastminute came to market in March 2000, turning the company from entrepreneurial pin-up to a symbol of dotcom excess.

That was unfair, because while the likes of Boo and ClickMango sank without trace, Lastminute weathered the storm, has recovered most of its float price and spent £30 million on acquisitions in the past few months alone.

But Lane Fox isn't the only once-garrulous guru reluctant to talk up the market these days. John Chambers, chief executive of Cisco Systems, wobbled the markets when he declared last week that future demand remained uncertain.

Yes, all the IT giants are reporting enhanced revenues. Yes, venture capitalists in Silicon Valley have an estimated war-chest of $100 billion to invest. But last time round they were forced to write down $25bn spent on fledgling companies, and their European counterparts $10bn. So, in contrast to the goldrush of the late Nineties, seriousness and sobriety are the order of the day.

'I'm sure most of us would like to think we were smart back then and that we haven't changed our view of what makes a good company,' says George Coelho with a smile. 'But of course we have.'

Coelho is European founding partner of Benchmark Capital, for many years one of the most active investors in technology start-ups. 'We've gone back to the basics of understanding businesses. We look for business models that will stand the test of time and provide things that people really need, we want management who have done it before, and we look at whether or not the new technology advantage is really relevant.

'We want businesses that are financed properly and are selling things at a profit in real money. Above all, we don't view them as different from other businesses just because they are dotcoms.'

In the new climate, says Coelho, the ideal company - and one Benchmark has invested is - is Kalido, a data storage software outfit originally created by Shell then spun out of the oil giant. Based in London and Boston, it already serves the likes of BP, Unilever and Philips. 'The thing I'd like to tout about Kalido is that we already knew it had worked for Shell, that it had worked for real customers and would adapt when you changed data models,' Coelho says.

He admits that the pace of work is quickening: 'Six months ago, if you looked at a good proposal it would still be there six weeks later. If you look at it today, you have to jump on it or it will be gone.' But he is cautiously optimistic that valuations will be more sensible from now on. 'The downturn was so traumatic, I think the upturn will be rational. Although it's very hard to tell if it's a bubble until you're in it, and everyone loses their mind and forgets history again.' He confesses to some concern about 'a few companies floating in China and Asia that are extreme valuations'.

It's worth remembering that quite a few of the most famous dotcoms have thrived despite a slumping share price. Some still had cash to spare when the fundraising climate froze, which gave them a great competitive advantage; others just had good business models. Ebay, the auctions website, and the online bookseller-turned-shopping mall Amazon are reporting dramatic increases in sales, especially outside the US.

Meanwhile, those redundant broadband cables laid down a few years ago are finally being put to use as high-speed wireless networks evolve, and with ever-growing usage the internet is finally fulfilling many of those grandiose predictions of old. 'Old media', from Kodak to music labels, will testify to the number of people sending digital photos to friends or downloading music to iPods.

Microsoft, IBM, Dell, Cisco, Intel, Nokia and Apple are among the US com panies to have reported strong revenue growth in recent months. Industry cheerleaders can even rejoice at an old-fashioned takeover battle, with Larry Ellison of Oracle upping his hostile bid for Peoplesoft to $9.4bn. On a smaller scale, British companies such as chip-maker Arm Holdings and NTL, the once-stricken cable firm, are also resurgent.

In the case of the American giants, there are a couple of provisos. The first is that their results have been flattered by an exceptionally weak dollar, which makes non-US sales look better than they are likely to stay. Factor that in, and IBM's 9 per cent revenue growth, for example, is less impressive.

But more important is that the crucial 'business-to-business' market remains depressingly flat. 'The green shoots are there, but all this demand, whether in computers, notebooks, mobile phones or online retailing, is consumer-driven,' said one analyst. 'When there's an upswing in corporate demand, that's when we'll know the recovery is in train.'

Companies still account for the majority of technology spending, and sustained double-digit growth in the IT sector is probably impossible until corporate clients start spending money on computers again. The long-awaited 're-equipment cycle' predicted for blue-chip companies has yet to materialise. Most are forecasting only modest increases in their technology spending or research and development budgets.

So Wall Street and the City are trying not to get too excited. Meanwhile, audiences Stateside are being treated to the daily spectacle of their 'domestic goddess' Martha Stewart on trial over her controversial 2001 sale of shares in biotech firm ImClone. Still suffering from its dotcom hangover, America may not be ready for the next bout of irrational exuberance.