Same thing here after updating to 4.2.2 Pro. I had to force quit.

Cmd-Q minimized the LimeWire window instead of quitting, and selecting Quit from the LimeWire menu had no effect.

LM was also automatically launched at startup.

From reading this thread, it seemed that after updating to 4.2 (some) preferences were overwritten.

In my case the "Shutdown" option was reset to after competed downloads and auto-lauch at start-up was on.

After resetting the "Shutdown" option to immediately, I was able to quit normally using Cmd-Q.