Deluge
Since a few days back Deluge (and also Transmission and KTorrent) has started to use too much of the CPU sources while downloading. Although the sum of cpu usage of each process is under 10 %, real usage is almost 100 % one core and 40 % the other core.
I don' know what causes this, maybe any new system update? I've also noticed that usage went back to normal while downloading of one large file (openSUSE iso image) finished, now I'm downloading one small file only.