That's what LimeWire does to OS X.x. It bogs down your machine. Lots of RAM will help, and I've seen workarounds posted here somewhere that involve using the terminal to take away some of the resources that Java eats up. It's getting better, albeit slightly, thanks to either LimeWire or Apple or who cares who, but it's not there yet.
I've turned down the upload speeds a bit in preferences to save a little for browsing, and disabling Ultrapeer stopped mine from crashing. Even though LW techs insist that it won't help, I can demonstrate reliably that ultrapeer crashes my LW within 5 minutes. Disabled, crash be gone.