64-bit desktop computing is surging (well, as far as Microsoft is concerned, that is). According to the Windows Team Blog,
As of June 2010, we see that 46% of all PCs worldwide running Windows 7 are running a 64-bit edition of Windows 7. That is, nearly half of all PCs running Windows 7 are running 64-bit. Compared to Windows Vista at 3 and a half years after launch, only 11% of PCs running Windows Vista worldwide are running 64-bit. With Windows 7, running a 64-bit OS is becoming the norm.
According to Wikipedia, the first AMD64-based processor, the Opteron, was released in April 2003. In the seven years since 64bit-based processors were introduced, Windows 7 dramatically help push the software side of 64-bit computing, in part due to decreasing costs of memory, OEM adoption and the Windows 7 Compatibility initiative. However you look at it, Windows is the OS to beat.
For free software, Linux distros still has a loooooong way to go…