Although I'd also guess Stuffit is your problem (I don't think the Mac BT client is written in Perl, and I'm pretty sure I used that version under 10.2 anyway), I'd recommend downloading Azureus and giving it a try if you don't have a dual processor Mac.
Azureus is more complicated to figure out how to use, and is a Java application, but has WAY more features, and in my experience works much better than the "official" BitTorrent client. Not that bad, anyway.
If, however, you have a Mac with two processors (G4 or G5) then you DON'T want to use Azureus unless you need its features--there's a bug in Apple's Java that causes crashes after a while with some Java apps that do a lot of networking, which is exactly what Azureus does.