[xhroot]

Presumably, one could download the eBook to every book they've purchased on Amazon, even if they no longer own the print version (e.g., resold or lost). I'm hoping O'Reilly, Manning, and Apress get on board with this, but I can see why they'd hesitate.

[dunham]

O'Reilly has been doing this for a while. They offer discounted ebooks (I think $5) for print books you've already purchased after you "register" them (via ISBN) at http://oreilly.com/register/

[koudi]

Don't know about the others, but O'reill's been offering this for a long time.

[amzpix]

Manning provides access to e-books in multiple formats when you purchase a paper book.

[thirdtruck]

Pragprog.com has done this for years, possibly since they began.