While my main development machine at work is a Desktop running Ubuntu,
I also have a macbook at home.
Up to now, I've been doing development at home using VirtualBox with a Ubuntu guest OS.
It works pretty well, but at times a little cumbersome - having to boot up twice, the Ubuntu OS isn't as smooth as Mac OSX etc.
But it means my environment is pretty much exactly the same, and almost exactly the same as the VPS I use for a few sites.
I'm just curious what others are up to, and especially how they test in multiple browsers.