I'm not thrilled about the price, but I would pay a premium for a PDF that was truly enhanced. That means (at least) fully bookmarked and a table of contents and index that are linked to the content. Save me time from doing it all on my own, and I'll pay for it. ADD VALUE.
Other things that would be great are further enhancements such as an interactive, autocalc Character Sheet; sortable tables; semi-regular updates with the errata; a bonus module (such as Talon Pass); printable Power, Monster and Magic item cards; links to appropriate areas of DnDi and this site, and so on.
It's a loser's game to think of PDFs as "like the book, but digital". It would be so easy to enhance these in such a way that they are easily worth as much as the dead tree versions. Despite RPGNow saying they are adding bookmarks and links, that's still pretty vanilla. If they (or someone) were to enhance these releases in ways like I outlined above, then they'd be worth the price, IMHO.