I have been using HTC Desire Z for 5 months now.
Pros:
The first striking feature is the QWERTY Keypad. Unlike other slide out phones, the unique Z swivel design allows to use the top most like of the keypad with ease
It has Android 2.2 Froyo.
It has good hardware to compliment the S/W
The touch screen is awesome, love the HTC sense UI
It senses if it is in pocket and rings louder, goes quiet if u put it upside down. It has a proximity sensor which saves power when u use the phone to your ear by switching off the screen
Cons:
The Z swivel gets weak if you drop the phone . Dont buy this if you want a strong phone