The usual suspects for memory eating, IME, are code weight and large cached data structures. The $menu structure in D5 is decidedly not small, for instance.
Thanks so much for stopping by, Crell! I hadn't considered the $menu structure earlier today, and that is actually a large part of what makes up UC. 
I'll look into locale, but my bet is we're just going to have to wait till the D6 update is complete. In the meantime, I may try to make sure someone is tracking our memory usage while we port so we can try to lower our footprint...
@greenSkin - sounds interesting... do you have any stats for a live UC site by any chance?
Joined: 08/07/2007