Things like boot process rarely break. Try something like filling up your root or tmp partition. That just seems to be a bit more common as far as problem scenarios go.
Thanks for the reply. I've recently started working for a large hosting company, so there's a reasonable amount of scope for anything that can go wrong going wrong at some point, so I wanted to be prepared in advance for as many eventualities as possible :)
I've seen root partitions fill up a few times, but in my own experience we've always been able to get in and clear out some space before it's knocked the server over. I'll look into it a bit further tho.
Cheers.
A.