I've noticed Bluefish getting a lot of attention lately, particularly in light of Adobe's acquisition of Macromedia and the proposed combination of the two most popular editors in the marketplace today - Dreamweaver (which I've used for 5+ years) and GoLive (which I tried several years ago and thought was horrible). I'm actually loathe to give up Dreamweaver, particularly due to the great plug-ins for the PHP packages that let me add code for dynamic pages that I couldn't normally do without help from my programming staff (I've always been more of the "idea" guy).
Bluefish looks intriguing though and it would be nice to move to an open-source editor. The possibilities for add-ons to these types of projects multiply exponentially with the community growth around them. I won't be switching until they come out with a graphical editor, but I see that right around the corner.
I've been a big fan of DW for a long time but find the MX version to be buggy for some of the things that I do.
This doesn't run on windows, so unless you're running gtk on some unix/linux variant there's no real chance of trying it out. Luckily they've at least got a mac osx port that us apple users can try.