I'm guessing you won't have to worry about them overheating.
Just be careful when you make salad, that lettuce and tomatoes don't fly into any of the fans.
Haha no worries about overheating here! I can't tell you how many times my fingers have caught on one of those fans, it is so startling when it's dead silent and I'm trying to bundle wires. For anyone who's interested, the ambient temps are a constant 73 and the units have levelled out as far as temperature goes. They will fluctuate between 38 and 40 deg, but generally stick around 38 deg Celsius. To put that in perspective, these units were averaging 68C at full load before I inverted the blades and stuck those fans on. It costs about $50 more per unit to install the fans, but man does it give me some peace of mind.
I have been ogling the new Fast-Hash One 750 GH/s units over at VMC and am about 90% sure that I will buy one in the near future. I will be sure to post some pictures and might even do a setup walkthrough to make it easier on some of the newcomers. What is cool about the new FHO machines is that that they are USB driven, so I will be running a multiple raspberry pi raspbian+cgminer setup with them! My buddies and I are planning on some major expansion soon and I will do my best to document it all.
I have a buddy who is working on a neutrino particle detector (which one shall remain a secret, per his request) and he has some pretty great ideas as far as overclocking and liquid immersion setups go. It is up in the air right now as far as which directions we will take as we expand this project, but I will keep all of you guys informed!
