I know that this is going to sound like "I had a good thrashing at my public school and it never damaged me" but both my (and 'er) machines hibernate all the time. Only normally do a full restart if updating Windoze... or, all right, if Skype misbehaves again. Works out at two - three weeks, I guess. Talking about W7 pro and XP pro here.
But I guess it depends on how much 'stuff' one has running, and overheads and memory leaks an'all.