I understand the various positions represented here.
Mine is that I have an otherwise perfectly well functioning computer system running Win x64 with 8 GB of RAM that is fine for all my other uses, including Photoshop CS5. The system is less than 4 years old and is now being obsoleted, at this point, solely by Adobe LR4. As time goes on, I suppose other apps will also be no longer downward compatible, so I suppose Adobe is in the front of the wave. But, I am not applauding them for that. As everyone knows, it is a lot of work, not to mention the expense, to set up a new system, even if one is well organized. I don't like doing it any more often than I must, and doing it in less than 4 years is a bit too fast, IMO.