Henry Blodget (who was at the heart of the last dotcom bubble) advises we all proceed with caution in a Guardian article today:

"So why can't we all load the boat with net stocks, make back the money we lost five years ago, and retire rich? Why can't today's industry executives dismiss the 90s boom as a silly kindergarten recess and be confident that it is "different this time"?

Because, sadly, even the most powerful trends rarely proceed forever up and to the right. These days, it's easy to make money in internet-land, and when it's easy to make money, trouble usually lies ahead. What, exactly, this trouble might be - and when it might come - is hard to say. If it were obvious, the market would already have discounted it. Some possibilities certainly leap to mind: a global recession hammering advertising spending (which is usually among the first line items to get cut); click-fraud or a loss of exuberance hobbling search; Google's dependence on a single high-growth revenue stream, leaving it exposed to a stumble; Yahoo's continental drift toward its its new boss's roots in the movie business resulting in a more capital-intensive and slower growing business model; a loss of focus at eBay stemming from a high-risk bet on Skype. Any of these risks - and dozens more - could temporarily kneecap the stocks and leave investors wondering how they could have been so moronic to fall for the internet story again.

Or, in this second go-round, we might enjoy another five to 10 years of extraordinary, smooth growth, making the believers rich and leaving the cautious feeling like (poor) worry warts. One of the errors that people made in the 90s - one of the errors that I made -was to assume the trouble would be visible on the horizon before it wreaked commercial havoc.

Unfortunately, it wasn't then, and it probably won't be this time."