I put technical books into two camps: reference books and prose.
Reference books are like the "Python, the Definitive Guide" or "Web Development with Rails" and contain lots of code samples and snippets. Prose books are like Pragmatic Programmers or Joel on Software - they may contain some code, but the meat of the book is the narrative content.
For reference books, eReaders fail in my option (I've tried with kindle2/3) because of formatting and sizing issues. But for prose books, they are awesome and I prefer it to a pdf on a laptop. Another problem with reference books is that I like to be able to quickly flip through to find a specific passage - this is not easy on most eReaders (though you can try searching). I also miss having the physical copy around my desk as well, there is less chance for a coworker to notice the book and ask to borrow/discuss it.
Most technical publishers offer epub/mobi downloads of ebooks - I know Oreilly and Pragmatic both do firsthand; I've had decent success converting PDF to mobi with Calibre if you need to it yourself.