I've got mono
Mono is an open-source platform for running .NET framework applications which I'd been curious about for some time, but hadn't gotten around to configuring on a system. Monoppix provides a live Linux CD that you just boot up and to get a pre-configured demo system running Mono on Linux. This removed my excuse for not checking Mono out. It works with Virtual PC 2004 and took me all of 10 minutes to get going (all you need to do is use the Virtual Machine Wizard to create a new VPC, start it up and capture the iso image downloaded from the Monoppix site).
I haven't done much with it (just some simple programs and playing around) but it seems to work great. Highly recommended if you want to see what Mono is all about.
p.s. It looks like Mono Live offers the same kind of thing, but their web page didn't work when I tried to investigate further.