I've noticed that, since updating Ubuntu to 10.04 (from 9.10, which brings KTorrent to 3.3.4 from 3.2.4) that KTorrent is using alot more memory than it used to.

Previously, KTorrent always used less than 60 MB of memory. Right now it is using 227.8 MB and growing (slowly).

Is there a memory leak in this version?

228.1 now.

Edit: It also seems to have more CPU usage. It's steady around 12% (with no traffic going in or out).

I'm running latest svn and there is 176M used with 1 dl and 1 ul, but this includes also shared parts, so maybe it's not that much.
The heavier cpu usage is also noticed here - leaving ktorrent overnight and it will eat 50% of cpu, which causes my computer to go from powersave mode
and becomes loud. CPU is an athlon64 2800+, not much but it used to handle ktorrent in past without such struggle.

I'm not aware of any memory leaks at the moment, and CPU usage seems to be pretty normal here with 4.0.

CPU usage seems to start rampaging after enabling uTP protocol. Now it's back to normal.

µTP does create some extra CPU usage, but it should remain reasonable.