I'd also be interested to know this, Although from reading everywhere I can't find any solid info on it. It was suggested the update would come at the very end of June, but how long, or IF O2 decided to port it over to their handsets is anyone's guess.
If your HTC Desire is from O2 you may have to wait until (a) Google finally deliver it OTA (over the air) at which time Nexus users will get it, then (b) HTC have to test it with Sense before they ship it then maybe (c) O2 have to approve it. Could be a long wait.
you should see the pressure on the nexus support forum to get this thing done and shipped. HTC surely have early releases but the final version will ship to them, my guess, about the same time it starts OTA. So HTC will still have some testing to do.