My log file is currently at 41M. I've deleted it before but is there any way for KT to manage the size of the log file, or do I need to use the OS for this?

Currently, there's no way managing log file size. Maybe we can add some checks, but how did you manage to get 41MB log file?! How long was your session?

It would probably be a good idea to add an option to limit it.

I leave ktorrent running 24x7. I can turn off some of the messaging, to lessen the log size. Right now it's tracking all messages in the system section, all IP Filter, and that's about it.

I killed the log file about two weeks back when it was 16M, and since then it's gone back up and is at 53M now.

Turning off some log messages won't make your log file smaller. ALL log messages are written to log file, those options for turning off some messages are just for display in LogViewer.