As I've mentioned in previous posts, I've been using Linux at work for about 9 months now, and switched to Ubuntu from Red Hat Enterprise a few months ago in hopes of having GUI configuration of multiple monitors. The version of Ubuntu that is the newest officially supported one (Feisty Fawn) has no such tool, but the release that is coming out next month (Gutsy Gibbon) does:
And this goes officially beta tomorrow! I'm excited. Of course it's been available in alpha form for a few months now, but the development process is moving along towards the release date next month.