I've got the memory tweak running a command line window on my iMac, which has 640 MB RAM. I also have a Pismo with 192 MB RAM.
The input into the command line for the tweak follows:
cd /Applications/Ubero
java -Xms300m -Xmx300m -XX:NewSize=100m -XX:MaxNewSize=100m -cp Agent.jar ubero.agent.Agent -text
Presumably, this means that the computer allocated 300 MB of RAM for Ubero. This works fine on systems with 512 or more, but on systems without heaps of memory, I doubt it will work effectively, because the app will be constantly swapping data to and from the HD. So I changed the small number to 40 and the large number to 120 for running on my Pismo. Should I get any speedup from this more modest tweak? Should I bother, or just run the GUI?