as MoDaCo would tell you, the first 5 iterations were very problematic. with Alpha7 i'm not having any major problems. the 2 features that aren't working as they should are Bluetooth pairing with headsets (you can pair with a computer, tho) and native USB mounting with your PC. a workaround exists for the USB mount/dismount. there are also some features/functionality with native Android that don't exist on the Desire ROM (or i haven't figured out how to enable it, lol). the native Exchange email, calendar and contacts features and the visual notifications (e.g., msg counts) were just to much for me to resist. i really liked HTC Sense on my WinMo device and like it even better on the Nexus 1.
anyway, i wouldn't recommend trying it until it's titled beta and/or it's based on the production ROM. if you do venture to the dark side, be sure to read and understand what you're doing. and most importantly, WIPE your device before installing. if you don't wipe, you'll have issues. notwithstanding the Bluetooth headset and USB Mount issues, it's still stable enough for me to use on a daily basis (as of today, this moment, lol).