Since upgrading to Oneiric I am seeing this. I am not using torrents, only Firefox. One minute I have 700 MB free, or even 2+GB free...the next moment I have 37 MB free! Then a minute later, zero bytes free! I delete some files, free up some space, and then a few minutes later, 0 bytes free again! I fscked the fs, and then I had 2.9 GB free. But a few minutes of Firefox and, bam, 0 free space. This is crazy. It never happened with Natty, but as soon as I upgraded to Oneiric, boom. This is utterly unusable.