I've only had two stocks at the start of an IPO and sold them both quickly.
I was offered shares of Vonage at something like $17 and sold at the open for $14 since it was moving the wrong direction. And I had shares of 3COM (not an IPO) at $32 that rocketed upward as the company's PALM spinoff approached. I sold my 3COM shares at $102, $105 and $109 in a matter of minutes. Seconds later... so quickly that I didn't even see it happen... the stock hit $129, then fell to $105. I left for work and I think both PALM and COMS were down in the $80s or $60s by day's end. It was quite a bloodbath. I think one of them fell into the $20s and I don't know how far the other eventually fell.
I give my wife a hard time every now and then because she says we were offered IPO shares of EBAY - but she never mentioned it to me and we didn't acquire them. I think I would have gone for them. Knowing me, though, I'd have probably sold them too quickly. Except for that 3COM/PALM story, it always seems as if I sell winners too early and losers too late.