I would recommend a high-quality 120mm fan pointing directly at the heatpipes with the side of the case opened. I was able to lower the GPU temp by 11° Celsius under load.
I haven't tried the 480 GTX in a closed case and I believe that extraordinary measures will need to be taken to keep the GPU cool in that situation.
I would really like to see MSI offer a "Twin Frozr" model.
In this type of configuration, an EVGA GeForce 260 216 Superclocked ran at 91° C under load, while the MSI NX260GTX OC ran at 77° C - with the fan speed forced at 40%.
For those looking to purchasing a high-quality 120mm fan, you can check out this roundup at MadShrimps. They compared 35 models.
Just trying to come up with effective cooling solutions for those interested in moving to a 480 GTX...