There Aren't Many Venture Backed IPOs

If you don't include time, this graph is worthless. It's not just the exit amount, but how long it took you to get there. I think PG pointed out at Startup School that super-angels seem to be going for quick M&As, not IPOs, and that therefore, didn't care about the valuation as much.

I really like Fred Wilson's blog. But I'm wondering - he reckons there's a bubble in startups at the moment, should he be trying to exit USV investments [1]? I understand his complaints from a series-A investor perspective, but many of their portfolio companies are well established (Twitter, Meetup, Covestor etc.), why aren't they making a move for an exit?

[1] http://www.usv.com/investments/