My main workhorse machine is running Arch linux, really appreciate the philosophy of the distro.
Secondary is a Mac Mini, mainly for graphics work, and compatibility testing things not available in the Linux world. Keep a bootcamp install of Windows on it as well primarily for testing IE. The new Minis in particular are very capable little machines.
Just got a netbook, which is running CrunchBang linux. Great distro, lean and runs great on a netbook while providing the full Ubuntu resources. Will likely end up setting Arch up on it, just need to find the time and Crunchbang was faster to get started with. Really do like the CrunchBang config (openbox, tint2, etc) and will likely borrow from it quite a bit when I make Arch the underlying distro. Agree with bloodstarstudios, netbook works great for dev work, at least the text and web based portions.
On the server side, I’ve typically run Debian on my VPS instances. I’m considering Arch for that as well, although I would want to adjust the package management settings quite a bit, as a rolling release system the default behavior isn’t as ideal for a server.
I suppose my bias towards Arch is pretty clear