Depends for me too !
I gladly re-read some of my pbooks, and these ones I'd like to have as ebooks !
So when I can (when I find them, and they're not too expensive !), I buy them as ebooks too.
For example, I used the Fictionwise Sale as an excuse this week-end, to buy the Farseer trilogy, and the Barbed Coil !
Another example : I have Pride and Prejudice on paperback since I was 17, and it was one of the first I had as ebook too (and I bought the special Penguin ebook version some months ago !)
BTW, I'd like to have the books of my favorite Sci-Fi french author as ebooks as well (it could be possible, as he got back his copyrights from his former publisher), but presently, unfortunately, it seems the priority is for his new books (only on paperback too !
)
New technology, it seems !
Edit : Oups ! Forgot the LOTR trilogy, but it's a special case, because my paperback version is in french, and the ebook version in english !