There are plenty of programs that do not run on any 64-bit version of Windows, and as this is a home machine I will be using it on first, I will be using a lot of software that is among that group, namely DirectX games (though there are some non-game programs that I have to keep 32-bit XP Pro around for too).
If I can't dual-boot 32 and 64-bit Windows 7 on the same computer without requiring two licenses, then I am done wasting my money on Microsoft products. Vista 64-bit was already a huge disappointment, giving me nothing usefull for my hard earned cash other than the ability to run DirectX10 games, which is not really all that important to me as I prefer substance over "bling" for my entertainment dollars, and the ability to keep getting support since XP support is gone.
I can have practically every usefull feature of 7 and more (like non-generic drivers
in VMs) using Linux, and I can dual boot 32 and 64 bit versions, both for free. Plus I can develop my own software without having to pay Microsoft again for the right to do so. So why would I fork over the price of two operating systems when I will get virtually nothing for it that I can't get elsewhere?