jluke, you have fallen into the all too common trap of relying on RSS statistics as a measure of memory usage. RSS means "how many pages of memory did this process use". This number includes shared pages. Now, I think it's a reasonable assumption that alot of pages from libgnomeui.so etc are paged into the system without the Mono application in question. What you really want to count is how many private pages get into memory. This is much harder to measure, in fact, we don't have the tools to really do this correctly.
That being said, there are other reasons not to use Gnome#, one of which being that better versions of the stuff in there are being moved to Gtk#.
If you are thinking about measuring the amount of ram a process uses, please, please, please be careful about what numbers you look at. It's really easy to come up with nutty conclusions.