I think everyone can agree that it's booming, in much the same way that the housing market was booming. Tech is sexy again, and that's driving investment and throwing money into the ecosystem that otherwise wouldn't be there. That said, the only real test of bubbledom is whether the valuations are sustainable, and whether startups generate profit commensurate with the money being sunk into them.
Google, Apple, and facebook aren't going to continue making $65MM talent acquisitions indefinitely, so at some point the penny will drop. When it does, the question of whether we'll have a popped bubble or an adjustment will be decided on the individual financial condition of the startups in question.
Could the current ecosystem be sustained if Google, Facebook, Apple, and AOL acquisitions were no longer a reality? No. Too many people are investing in features, not companies. Those startups can't survive on their own if there isn't a real possibility of a big exit through acquisition.
Nevertheless, it isn't 1999. Groupon is IPOing with at least some real revenue and exponential growth, and LinkedIn has a solid, if not expansive, userbase. If there is a bubble, it should only affect the startup world, and even then only the companies that can't survive on their own.