I am running CM6 on my Desire (T-mobile UK) and I'm loving it. Having ran it on the G1 prior to this my expectation was big and I have to say that this has excelled it.
For any body wanting to give this a try be sure to pop to CYANOGENMOD.
You must have root access first but all the help you should need is on this site. These guys eat, sleep and breathe Android and have some of the most amazing developments crammed into CM6.
The full changelog can be found here.
