I was a bit taken back by the memory consumed by the WinHEC build of Longhorn. It turns out WinFS is sucking up around 200mb of RAM. Well, as of right now I'm not planning on learning much about WinFS (nor do I have the resources in a VM to properly take advantage of it), so let's get rid of that sucker. To remove some components, I had to edit the C:\WINDOWS\INF\SYSOC.INF file (do so at your own risk, I'm just kinda winging it here in a VM, so I can easily start over). I had to remove the HIDE keyword from entries to be able to uncheck them in the Add/Remove Windows Components dialog. Once I did that I was able to go into add / remove items, and uncheck WinFS. 200mb of memory almost instantly reclaimed.
Once again, WinFS seems really cool. But I'm not going to be playing with it in a VM, so I decided to get rid of that sucker. Something else that seems to have helped out performance (especially in Explorer) was turning off :preview and filters in folder." You can find this option in the advanced section of the My Computer Properties under performance.