I always make my OS look like that anyway, personally. I don't see the point in fancy UI. And the memory it used wasn't that bad, it probably was using more memory than it seems at first glance, but in the taskmanager I only saw my memory usage increases by 50mb between old win95 look and Vista look.
(it certainly uses more power too, but since you talked only of memory, I'm just mentioning mem)
There is a lot of bloat tho (outside of Aero), my memory usage after a clean install with vista is twice what XP was. Something like 600-700mb used instead of 300-350 in XP.
(I'm trying to find a good guide of what I could disable in Vista that I don't need, but searching for stuff like that in google gives me results on how to disable UAC-only 99% of the time. I'll just keep on looking I guess.)
If you wanna talk about ridiculous tho : Move a window around the screen really fast (like in circle) or even just move the mouse ALONE.
Then look how much CPU power that uses... Horrific.
(this goes for the old win95 look too, it uses way too much cpu power)
But I'm just wondering, what are you talking about when you say 20gb Phil? =/ You mean the space Vista takes on your PC? (Mine doesn't even weight 10gb)
(Even tho Aero looks kinda nice
and I didn't feel any real slowdown between XP and Vista when dual-booting, I still prefer using old UI just to be safe.)