I don't really need an eReader for programming books. Most of the time I'm better off reading those at the computer where I can play with the code in them. For that, I can just buy the PDF and read it in Foxit.
I'd want an eReader more for fiction, and fiction definitely still prefers DRM over non-DRM.
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 . . .
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.