So, a friend of mine bought her 17in MBP in yesterday because her trackpad seemed to be playing up. Indeed I had used the machine in the past few months and thought that the track pad felt odd in operation but didn't think much of it.
Anyway, now the whole back was stuck and you couldn't use the cursor at all.
I flipped the Mac over and was horrified to see the whole battery was distorted and bulging outwards. Obviously the battery was pressing on the inside of the trackpad. Removing the battery returned the track pad to normal operation but the battery was obviously in a bad way.
Only a week before it had shown no external signs of distortion.
An hour on the phone to Apple resulted in a free exchange battery despite the Mac being out of warranty.
I knew about the 15in battery issues but didn't think Apple had issues with the 17in machines but there was some evidence on the interweb of an issue here, although the Apple guy seemed to think it was a one off.
I guess a few more days and it could have been exploding laptop!