Update 5-23-09: There is now a dedicated website for this process. Everything you need to know/download/do … all in one spot.
As of yesterday, I have a ~$400 Dell mini 9 netbook running OS X 10.5.6 and the process could not have been more streamlined. In fact, according to the experts on the Dell mini forum, the process for installing Mac OS X Leopard on the Dell Mini has been so finely tuned that users won’t usually notice any major differences from a typical OS X install process. Hardware such as audio, video, and wireless networking are all enabled and working great. The Dell Mini is probably the most OS X-Compatible non-Apple hardware available right now.
My experience was that in roughly 2 hours, with 2 USB drives and a original retail OS X DVD, the process was seamless. Plus, you’ll experience the fun of pasting the Apple logo that comes with the OS X DVD over the Dell logo on the Mini 9. I find that the Dell mini 9 forum (link above) was the most complete set of instructions. Highly recommended.