Matt Pietrek has a new article published on msdn, called Everything You Need To Know To Start Programming 64-Bit Windows Systems. It’s a pretty good overview if you haven’t come up to speed on this yet, but it is annoyingly light on some of the driver-centric issues.
I can personally attest to the WOW64 registry redirection thing, though – I just spent an embarrassingly long time fighting with WinDbg, trying to get it to post-mortem debug some 32-bit usermode code I am working on. It turns out, obviously, that windbg -I only installs it in one place – i.e. 32-bit windbg installs itself only for 32-bit post-mortem debugging. I had installed only the 64-bit debugger on that box, and it took me forever (and eventually a justly condescending reminder from Ken) before I figured out what was up.
The Pietrek article also links to another that looks interesting at a glance, but I thought I’d pass it along too: X64 Unwind Information. Enjoy!