I had an HTC Desire Z until last July when I upgraded due to a bad battery. It was running GB even though ICS was out. Personally, I did not see any features of ICS that I really had to have. I was quite happy on GB which I got around August 2011. I think a few months later I got another update that fixes a few things.
Had my battery not gone bad, I would still be using my Desire Z now. My contract would have ran out in March of this year. I did fire up my old phone a few times just to test some app updates. I can pretty much use any app I currently use on my current phone (SGS3 running JB).
I guess I just don't understand why people have to have the latest version of anything even if an older version works for them. It's not like a phone running GB is unusable. You can still run most of the most popular apps that people use. I see so many people on tech forums who think their phone is a POS the moment a new version of the phone OS comes out that they cannot get immediately.