Ok, so some news, after running with a fresh svn checkout of kde 4.2, and (for
sure this time) the 180.16 drivers, plasma is up to 105MB of pixmaps. Its
slightly strange too, it only started increasing after I stopped playing with
things trying to get it to allocate more memory.
I've just did a little silly test of recording X memory use in various stages of X and kde restart
Virt Res Shr
Full Dekstop: 629M 318M 9336
Loged out: 201M 131M 7728
X Restarted: 123M 54M 7504
Full Desktop: 496M 195M 7856
Clearly it looks like X isn't freeing some of the ram, though most of it is gone.
I'll be testing with the open source nv driver next to see if it also shows leaks, and if they are as bad, well its most likely plasma's fault.