Had to reinstall my os x on my air via the pen drive (went very smoothly, was very impressed btw) after a weird thing happened, see if anyone can shed some light.

All of a sudden with no apparent intervention or tweaking by me, my hd starts showing low space, I keep deleting and deleting (and getting system force shutdown prompts) and at one point I realise that as soon as I start up os x, and do a get info on the hd it starts incrementally decreasing the stated available space...quite strange, and I did quite a few restarts, it's not as if it might have been some background process....

I can post the console logs too.