I'm a pessimist and spotted every recent bubble. What is a bubble? It's when value becomes detached from "objective" financial models. This may be the case for a few high-flying businesses right now (Twitter?), but not widely. The recent funds from Goldman and JP may push valuations for Facebook & Twitter beyond reason because they are chasing a few shares in private markets. But throwing a million $s at a few stupid startups isn't a bubble. That's the VC industry buying lottery tickets. I don't think there's a bubble. There's just a little excitement in social media and mobile apps.