Marc Andreesen argues it's not a bubble because the big tech companies - Google, Apple - still have sensible P/E valuations and anyway it can't be a bubble if everyone calls it one. Let's look at some counterpoints.
Facebook, Zynga, Zipcar, LinkedIn, Demand Media, Twitter, iwantadoor.com (yes indeed) and yesterday's big story, Groupon.
What makes all these companies signs of a bubble? Everything is priced as if this market has no losers. Everything is priced to win, win big, face no competition, face no meaningful downside risk and not "do a MySpace".