I've been using the HTC Desire for about a month now, and I'm very, very satisfied with it. Purchased in the US to be used in Brasil, it is working wonders with a local service provider SIM.
First off, the phone's design is not as groundbreaking as the iPhone - to me the iPhone 4 is the best looking phone so far - but it's not without its qualities. It has a clean and discreet design, and I like it that way.
The Android OS with the Sense UI runs very smoothly with the 1 GHz processor built on this phone. The applications run slick, and no problems in multitasking. The screen is very sharp and very bright, the touch control is fast and accurate, pleasant browsing experience and lots of apps to boost your phone from the Android market.
Call quality hasnt been an issue yet, no dropped calls so far. Signal reception is good, and call sound is... well, ok for a phone. The music player is very good, although it lacks an equalizer (I dont really miss it though, because music playback quality is good enough without EQ when using a better pair of headphones than the standard - I'm using the Klipsch Image S4).
I highly recommend this phone to anyone who wants to steer clear of the control freaks at Apple, without any sacrifices (look for the reviews around the web, some sites rate the HTC Desire higher than the iPhone 4, and that means something).