Other than the ability to carry a large library around with you the Kindle is pretty sucky for Programming books - the screen is too small and the formatting too limited.
I think a good market for this is in areas with long, public transportation commutes. Those who take the car to work have fewer good use cases for e-readers.
So far, I find the Pragmatic and O'Reilly ebooks to be pretty nice on Kindle. Code examples don't always look super. But I sometimes landscape the view (especially on pdfs) and it's much better.
But I also tend to read and hack separately anymore these days - reading to drink the bigger picture, then hack and use Google as my language reference . . .