Twitter and Color are startups with no clear business model. Groupon and Google are going concerns.
As per the blog entry: "A bubble is a decoupling of asset prices (valuations) from their underlying economic fundamentals". [Agreed!]
Throwing $45 million at Color with nothing more than an idea and the hint of an app is evidence of a bubble. So is Twitter's recent $7.7 billion valuation based on a predicted $150 million in 2011 revenue.
I know it hurts - hell it's going to hurt all of us - but you better believe it. Prepare to be profitable or die.