IANAL
From back in the Napster heyday, what I remember of the discussion is that it is unlawful to download an mp3 of a song for which you own the CD. You may lawfully burn your own (not sure how/if the DMCA changes this). I would assume the same holds for print vs. PDF.
For myself, my Amazon order will be a month late. BN.com doesn't have any in stock, neither did the other couple on-line spots I checked. The local stores don't have any copies. I am pretty much SOL in locating any legal copy of the books, right now, but I have kept my order on Amazon. I also intend to subscribe to DDI and buy the official PDFs of all the hardcovers I buy from WotC (assuming they were serious about a minimal price on the PDF, otherwise, I'll just use the dead trees).
Meanwhile, I'm doing my darnedest to pimp 4e to my current 3.5 group. To my knowledge, none of my players has any illegal music or books and they will buy the core rules, if we convert. If WotC asks me to stop promoting their stuff, I will -- I'm sure the extra month isn't going to cause me any undue hardship.
Sometimes moral and/or ethical do not share the same space as legal.
You will also, please, note that I did not say I have the PDFs of the core 4e books. Nor did I advise anyone to torrent them. That I would definitely not do because there are plenty of people, I'm sure, who would get the PDF in place of the actual book. There are also a few people who would rather spend a few hours downloading the PDF, then spend $40 each on the the paper and ink to print it out than to spend $25-30 on a nicely bound hardcover. I don't understand those people, but that is neither ethical nor legal.