I'm personally HAPPY that we're not in the middle of IPO fever. I remember back in the "good old days" of DotBomb when everyone and their mother IPO'd. Profit, cash, revenue didn't matter. Simply hire a bunch of computer people, install a basketball hoop in the middle of the office, and IPO! We'll all make MILLIONS!
Rather than attribute the lack of Seattle IPOs to a weakness in the Seattle Tech Economy, I'd be more likely to put it down to weaker stock values. The people running the IPO (executive teams and the board) are all sitting on tons of options and stock and are probably pricing their personal fortune in Summer 2007 stock prices...
Just a theory...