Good!
With such a positive experience using CyanogenMod 7 on my HTC Desire HD compared to the stock ROM that shipped with the phone, there is no way I would ever buy an Android phone ever again unless:
a) It was relatively easy to install a custom ROM (ie, unlocked bootloader)
b) A decent custom ROM existed for the phone (ie, CyanogenMod or good alternative)
The difference between the stock ROM and CM7 is night and day, I've even run 'Android Revolution HD' which is just a highly optimised version of the official HTC rom and even it runs rings around the stock one. Clearly HTC didn't spend too much time polishing it.
+ Overlocking and the ability to flash newer radio code is something which I really like.