Delrin AF does make a pretty good leadscrew nut. We have used it in several of our products. If you are interested in a easy to manufacture anti-backlash type nut, take a look at the PDF catalog at
http://www.neat.com/techinfo/downloadform.asp
The info on the nut is on page 243. It is a split nut with spring preload. There is also loads of information in the technical section of this catalog, and I should know, as I work here. :-)
Keith