I'm thinking I'll put VMWare ESXi on it (it's free) and pull in my existing Windows server as a guest, and then set up a couple more linux guests so that I can start experimenting on migrating everything off of the Windows server.
Assuming things go as planned, it should get here around Halloween. Maybe I'll get it some orange accessories :)
The server is from the Small Business "10 days of deals" promotion, and is available for today and tomorrow if anyone is interested.
It's $199 after $399 off of the regular price, and you can put in a limited amount of upgrades (it takes a maximum of 4GB RAM, and it's a single-socket machine that takes a dual-core processor). It does have two 32-bit PCI slots and three PCI-e slots, though, so it should be more than sufficient for me.