I don't think I have a slow machine but every time I open Outlook, I keep thinking that it might be time for an upgrade. It got me thinking that it (and many other applications) could benefit from a "load in the background" option. The idea is based on the desktop search apps that index your machine while it's idle. Outlook could start loading at startup (and I must stress, while the machine is idle) while I browse the internet, load up Visual Studio, etc., etc. Then when I actually click on the icon, the app might be a little snappier.
Without something like this, I'm giving serious consideration to making GMail my primary mail client.
Kyle the Impatient