(Trying not to make this a 'me too').
Me too! Ubuntu 10.04 (upgraded from 9.10) and ktorrent hanging entire system when checking. Happened three times today, last time I was running nothing else (well, obviously background stuff, but no other apps open). Had a sudden thought about disk space so opened a terminal but it hung just before terminal opened.
Encrypted home drive, and yes I didn have plenty of space (around 20 gigs).
Most annoying thing was I was trying to download the Ubuntu ISO via the torrent :P
Transmission worked fine though so if anyone is having problems that is at least a work around.