I picked up a used first-gen Macbook Air, spending $460 for a beautiful ultraportable with passable tech specs. I immediately noticed two issues: high heat and a slow hard drive. My MBA put out around 80° C when idling, 100° C under load, and the fan churned constantly at 6200 RPM. Boot times were around two and a half minutes, and even when the OS X desktop finally appeared, another 60 seconds elapsed before my login items were loaded. Something had to be done.
The repair process was quick and easy, thanks to expert repair guides published by iFixIt. I found the video teardown especially helpful; MJ's glowing tresses provided me with the confidence I needed to take apart an Apple notebook.
Once everything was disassembled, I was shocked to find that someone on the Foxconn assembly line had applied a entire tube of cheap thermal paste to the exposed dies. The goop had run well off the edge, and all of it had physically deteriorated quite a bit under the high heat. I cleaned everything up, reapplied an appropriate amount of Arctic Silver, installed a 128 GB Sabertooth ZF SSD, and sealed her up. Presto!
My system is lightning fast now and actually feels brand new; complete boot in under a minute and idles around 50° C @ 1800 RPM. Any owners of the A1237 should very seriously consider performing a similar repair; I am absolutely loving this laptop now that it's cool enough to put on my lap!
For me, the proper tools made all the difference. In particular, I highly recommend the pro magnetic pickup tool, the Petzl LED headlamp, and the plastic sorting tray. There's a ton of extremely small screws inside the Air, and dealing with them is far easier when you've made the appropriate prep steps.