All I can say is based on my experiences from running Windows 7 over the past year (Basic, Home Premium, Ultimate & Enterprise, Beta, RC1 & RTM) on multiple computers, both laptops and desktop, is that the OS is far and away better than the one it is replacing. And my experience on Duo Core and Quad Core computers leads me to conclude that Windows 7 utilizes FEWER resources that Vista (on average 256MB on start-up) , is more stable, and runs faster, on both 32-bit and 64-bit clients.
Microsoft has announced that it will stop supporting Windows XP in the near term and that means no more security patches, hot fixes, or Service Packs. All too soon the OS will become obsolete despite its support for 64-bit computing.
I am recommending that my customers move to Windows 7 on a case-to-case basis if it makes sense for their business. But if I am putting in new PC's for clients, I recommend Windows 7 because I truly believe it will improve overall productivity.
I am looking at more than just the desktop experience, I am also considering how Windows 7 interacts with Microsoft's Network Operating Systems to help improve security, PC deployment (Remote Installation Services), software pushes/installs, VPN, Outlook Anywhere, Outlook Web Access, and a host of other functions that Windows XP either lacks or only does grudgingly. Not to mention virtualization; yes small and medium sized businesses can take advantage of the technology, but not with Windows XP!
And for most small businesses Linux is not an option even worth considering.