It'd be great if Fluid's full screen mode work more like Adobe Lightroom's, namely:
1) Make it possible to switch between spaces in full screen mode, without falling back to a normal window.
2) Make the menu bar accessible while in full screen mode, either as something that always appears, or as something that drops down when the mouse is moved to the top of the screen.
These two tweaks would allow Fluid + Spaces to function like a series of single-task applications, which is really useful for concentrating on a single project or task. Perhaps the implementation of #2 would also help fix the "Bookmarks bar not working when in full screen mode" problem (
http://getsatisfaction.com/fluid/topi...).
Fluid's a great app, and it keeps getting better... There's a lot of potential here, and I'm excited to see where you take it!