I have a desktop PC with 6400 core 2 duo, 3GB RAM and 2mb broadband.
I couldn't agree more - Windows Mail is slow to load and then populate with emails. Strangely enough it seems to get a bit quicker the longer my PC is on - I think! Sometimes when it loads all the emails appear to be there almost immediately.
Definitely slower than Outlook Express with a P4 2.4 and 1GB RAM.