Phex is a Gnutella program which accesses the same network as LimeWire, but which is developed by another group of developers, who develop in their free time, so it isn't backed nor restricted by the need to make money.
It is a good deal fairer to your CPU (at least compared to LimeWires a year ago, I didn't test LW since), and it offers you some advanced configuration and other functionality not found in LW (you can get an overview on our features page:
http://wiki.phex.org/Features )
The problem might have disappeared over a restart.