I have done some work in an effort to keep it as cool as possible. I actually cut the entire back of the cabinet out to let in as much air as possible. Also I have a good 3 inches on the back of the cabinet and the wall to let plenty of air in. Finally whenever I'm actively using the computer I keep the cabinet door in the front open to let air in that way as well.
Thanks for the ideas, I'll have to see what I can do with the dryer hose. I think I actually have some extra laying around.
Do you also have side/top case fans? Those make a big difference on letting air in and out. You may just need to really have a lot blowing in, and have all the air coming out go through the hose and drop off a good distance away so it can't be sucked in again.
On my old system that I made to be as quiet as possible, I ended up doing that. When I hooked up the hose to it, it not only quieted it down, but it kept it pretty cool.