We've had a '96 Seadoo GTI since it was new, and it's still running like a champ to this day. I know a lot of people with Seadoo's and have never really heard of them having horrible problems with them.
One thing about jet ski's though, they will last if you take care of them. I know they are made to be thrown around and to have fun on, but little thingslike washing and flushing it after riding is what makes the difference.
My 10.5 year old ski: