I don't believe we're in a bubble (in the sense of a liquidity event) - but certainly the number of people who have never before considered starting a web business who are wanting to give it a go are coming back again.
Those people are here to stay for as long there are startups who make succesful exits and get talked about. The process looks so damn easy. Make a small app quickly using a nice platform like rails in only a few weeks and then flip it for millions. Why wouldnt you give it a try?
For example photobucket has built a ver impressive subscription business and facebook is finding interesting (in addition) to traditional ways to moetise its vast userbase (facebook gifts if projected to make $15m this year)
I just feel the cheaper startpoints mean that there will be sufficient darwinian evolution for the better startups to succeed. We're going to see more failures but less flameouts like pets.com or boo.com which took a lot of money but weren't nimble enough (because of the cost & state of infrastructure) to change direction.
I argue we aren't in a bubble.