Watch Crockford on Javascript at ydn: http://developer.yahoo.net/blogs/theater/archives/douglas_cr...
Watch @ryah on nodejs at ydn: http://www.yuiblog.com/blog/2010/05/20/video-dahl/ (and the other javascript related videos linked on that page)
It's not yet great for tech books, stuff where you have to jump around randomly rather than reading linearly, books with deep TOC.
I hope the quality of programming books on the kindle will improve in the future, but now it's not too bad if you buy the mobi/pdf combo. You can always use the pdf on your computer if you need to check something quickly and your kindle is not nearby.
For me, the biggest advantage of having programming books on the kindle is that you can easily carry a few 1000+ pages books around and get some reading done when you have some unexpected down time.
I feel that programming books on the kindle are particularly good when you're learning something new and want to read sequentially. It's not so great for reference as you'd need to jump around and that's not kindle's forte. (although I do use the pdf as reference)
Edit: I forgot to mention that O'Reilly has a 7 day return policy on ebooks. I only wish they had a ebook sample like amazon has.