Rather than force quit, wait 5-10 minutes. If you are downloading very many/big files, the verification phase can seem to lock up the program, but it isn't actually frozen. If you have been running for a few days, clicks can take quite a while before the screen redraws.

Open your OSX Applications/Utilities/Activity Monitor to see what LimeWire is actually doing. Often LW will respond after it has finished whatever job it's doing.

Also, look for the Lord of the Rings' posts about the java settings for OSX to see if they work for your machine.