So, with the advent of the new addon profiling tools in 2.1, it's become pretty obvious that KTM is spending a TON of time processing all its onupdate handlers per frame. This is due to KTM's design, which uses a brute force polling system, rather than an event-driven system, so there's a lot of additional overhead incurred when there's no work to be done.
So, on a whim, I banged out this mod this afternoon. What it does, basically, is disable KTM any time there's nothing interesting going on, reclaiming valuable CPU-per-frame time.
You can get it at
http://files.wowace.com/KTMCPUManager/KTMCPUManager.zip or through WowAceUpdater
It's basically about as fire-and-forget as they come. Install it and it does the rest. No config or anything to worry about.
On my machine, KTM consumes between 6% and 8% of my UI time per frame while CPU profiling is enabled. With the mod enabled, that drops to under 0.01%. This doesn't do anything to improve performance in combat, but you won't be wasting cycles sitting around Shattrath anymore, either.
Try it out, let me know what you think. Feedback is welcomed!