Overall, I would have to say this is one amazing device. It is just so usable .... I would never even consider buying a phone with non android OS again. After using Android the horrible nature of how other phones are crippled and designed for the carrier not the user.
I almost feels like I am at my PC.
There are really only 2 things that bothered me about the phone.
1) I am worried that HTC and/or Android may be caving in the to carriers. Noob me was under the impression that I could access Android OS much like I can do with XP and Win7, but the Desire Z is locked up pretty tight (there seems to be ways though). Carriers seem to have a irresistible desire to force things on you and I was hoping to escape that with Android. My Fido phone was designed like a highway to spend money at Fido and a deerpath for how I actually wanted to use the phone.
2) The classic example is the "Games" they included in the App Drawer that you cannot delete. I guess they are hoping that on average, sooner or later you will be bored enough to download and or pay for it when stuck somewhere and they made deals with the developers. Why do they do this? I can stand crapware as long as I can delete it, but when it is locked in, it just pushes me towards rooting my phone.
3) Web surfing is divine on the Desire Z but this brings me to the second worrying point. The web pages that come up are crippled in a very sad way. The classic example is IMDB.com. The phone version has a lot of the statistical data I like hidden somewhere where I can't find it. I bet much of the movie industry would like to get rid of this information all together especially user reviews and age stats, so that one easily manipulable number can be displayed.
Many Web sites adapt to the device (every Web browser sends it's ID and OS) so your IMDB issues are with IMDB. If you check the address bar, www.imdb.com redirects to m.imdb.com (the mobile version of IMDB).
I don't like how carriers try to lock you into their solutions either. At least you can root most Android phones.