Which brings me to this point: The next major releases of the big two OSes, Windows and Mac OS X, will more than likely have dropped support for 32-bit hardware.
In a way, that's not too bad, the last time 32-bit only x86 hardware was sold as a serious desktop was three years ago, back in 2007. Pure 32-bit x86 processors these days are limited to Atoms and embedded chips. But, there's a downside. For example, Asus is selling a nettop based on the Eee PC netbook hardware called the Eeetop. It contains a 32-bit processor, and although it sits shiny on store shelves today with a fat $699 pricetag, when Windows 8 comes out around 2013 or so, forget about upgrading to it - you'll find the Eeetop's 32-bit Atom unable to run the 64-bit Windows 8, which for all likelyhood won't be produced in a 32-bit flavor.
Before you say that this seems unlikely - think again. Microsoft's server and enterprise OSes have always set the trend for their consumer-class releases. Windows NT eventually replaced the classic Windows line starting with Windows XP, and as another sign of things to come, Windows 2008 Server R2 has already dropped support for 32-bit x86 processors, being available exclusively for 64-bit x86. Microsoft has been providing 64-bit versions of Windows since Windows 2000 for the Intel Itanium processor, however, it wasn't until Windows XP that 64-bit x86 builds were shipping.
And don't think that the Hackintosh will save you. I don't expect Mac OS X 10.7 to ship with 32-bit support, aside from user-mode backwards-compatibility (although it's likely that it can be hacked to run on older 32-bit hardware, since it will without a doubt contain 32/64 universal binaries of pretty much the entire operating system for the sake of backwards compatibility.)
However, I highly doubt that any of the major open-source operating systems will be dropping 32-bit x86 support anything within the next 15 years. In fact, I wouldn't be surprised if the announcement that support for i386 branch is being dropped in Linux arrives sometimes after 2070, with NetBSD following suit sometime around 2100.
Compare that with Microsoft, who, as I said before, seems to be dropping 32-bit x86 as early as 2013.