Yeah - I've basically come to the conclusion that the mobo just won't hibernate in Win7.
I suspect that the user's working patterns have changed,so that it's become noticeable, rather than anything else.
Looking through the relevant logs, Norton was installed on 1st April (apposite?), while MSE wasn't removed until mid June - the thing must have run like a slug in the meantime, but it was only when the main machine in the household started causing problems that I was called in for a twofer, with this one as the 'while you're here....' :)