I still believe the chance of Google losing or preventing access to my data is much lower than the chance of me accidentally screwing up my own server and finding out my backups don't work. It's a huge amount of work to get anywhere close to the reliability of GMail. You have to maintain the server, secure it, test backups, verify backups and deal with every security or maintenance issue that comes up.
It's a trade-off, and one I've come down on the side of GMail for.
As long as it's in Google's interest to provide such an outstanding service to their users, yes, that particular billion-dollar Top Coder champion-filled company will do a better job of managing a mail server than you and I combined.
It's a trade-off, and one I've come down on the side of GMail for.