He just mentioned on his blog Monday that he was trying to convert his backlist so he can sell them on the Kindle. What's more interesting is how he's getting the source files. He's relying on pirates.
The major problem with getting one's older works into electronic print is that few have electronic copies of the books. Having them scanned and edited can be expensive - not terribly so, but the costs can be significant, and usually involves destroying a printed copy so that it can be fed to a scanner. Multiple scans with comparisons can get copies arbitrarily similar to the printed copies; of course the printed copies will contain some typographical errors, so the author probably ought to do a final scan before reformatting for Kindle and iTunes publication. The temptation of course will be to do revisions: I don't know, but I suspect that "Revised edition" with a new introduction by the author would increase sales.
Norman Spinrad has discovered Amazon and iTunes publication, and tells how he found clean copies of many of his works on pirate sites. Eric Flint has often said that pirates are more helpful than harmful; many authors have disagreed, but this is a clear example of how some pirates can be useful. Of course in Norman's case there were pirates who undertook the work as a labor of love because they wanted to see his books in print, and they took care to do quality scans; many pirate copies of books are horribly done.
Meanwhile, Eric Pobirs and Peter Glaskowsky have been busy finding me clean copies of my fiction and some non-fiction.
It makes sense to me. A file is a file is a file.