iMac G5 iSight (2.1GHz), OS 10.4.6.

Version 3.9 of this marvellous app works perfectly for me – no hint of any slowdown with it or with anything else. I suggest you need to do some troubleshooting. Use DiskWarrior (if you haven't got it you should have!) to rebuild your disk directory. Use AppleJack or another reliable app to 'deep clean' caches and swap files. Trash all Norton/Symantec products. Make sure that Spotlight is not interfering. If you can't find (!) anything wrong you might try at least (re-)running the Combo Updater for the OS iteration you are running to refresh your system – that might not be the answer, but it can't do any harm and you never know...

The main clue that you are misinterpreting things is that in a Unix system one app, even if faulty, cannot adversely affect other apps. Do think again!