If you have OS X, I'll give my usual spiel with all OS X bugs. Go to jum's website http://baghira.han.de/~jum/ and download the latest LW version of the jum build. It has numerous minor bug fixes including reducing cpu and memory usage.

I agree with stief too on the 9 thing, sounds like a memory issue.

Another thing though, the app might be getting enough memory, but if the person is an ultrapeer, he/she might not have the CPU/memory capacity to handle it effectively even if it is getting the recommended memory.