Dennis recently linked to me from his blog, and I wanted to say thanks, and to point out a particularly cool post. Ferron's Guaranteed No Mess No Mixups Method for Swapping Rims without Relacing is something that I wished I had happened upon years ago.
The problem: you have a new rim, and you want to build a wheel. This task is typically a pain, though some people enjoy doing it.
The special circumstance: you already have an old wheel built.
The critical observation: in addition to re-using the spokes and hub from the old wheel, you can preserve the information stored in the old wheel's lacing.
The method: put the two wheels side by side. Transfer one spoke at a time from the old wheel to the new (in careful order), and you save your self a lot of hassel.
Well done Dennis.