Yes, yes, yes.
For my current gaming purposes, a pdf is much more useful than the physical book (even with the DDI, because fluff isn't in the DDI).
Not that I don't get by with my mix of physical books and scanned material, just that it's such a tremendous hassle, I would gladly pay for an easy way out.
As an aside, why doesn't D&D have its own Wiki?! It strikes me that for FFZ, I can look up almost anything in any FF game on the FF wiki, but for the D&D stuff, I need to reference about a thousand different documents. I mean, mechanics aside (though it could probably include d20 stuff), it would be so useful to have a quick historical glimpse of what, say, Orcus has been up to for the last 30 years of gaming history, and where the Dragonborn originated and how they changed, and that kind of stuff is too obscure for Wikipedia.