LimeWire does use a lot of memory. It will immediately want to grab about 30 megs since MRJ wants that much. Then I'll notice as time goes by the LimeWire memory usage continues to increase at least past 50 megs until my memory is so fragmented I need to restart LimeWire. I have 192 megs of RAM. Turning on virtual memory might reduce memory usage.

Also, LimeWire and many other apps will as necessary grab temporary memory that is not specifically assigned to it in Get Info. Applications can use this special memory to open really large documents without having to change memory settings. When the document is closed the memory needs be released. LimeWire might be opening large documents for uploads and downloads but when the transfers are done or whatever it is doing the temporary memory needs to be released.

This problem in general is also called a memory leak, when an application doesn't give back memory that it no longer needs. Memory leaks prevent LimeWire from running for long periods of time without restarting.

I noticed for LimeWire that when I increase the memory allocation in Get Info the added amount is assigned to the application but it isn't actually used (at least right away). The added memory functions more as a buffer.