I remember seeing a few cases of Google account de-activation every year. Not sure how often it happens, but it does happen. I personally use Gmail and really like it, I don't expect to have any problems with them, but I do know that my account being deleted at some point for no reason is a real possibility.

I think that email is a bigger problem as it's the main connection between you and all the other services you use online. Lose your email address? You're going to have a hard time recovering the accounts on all the other services.