I'm a teen who usually sends about 50 to 60 texts a day, and I can say that this phone has never let me down at all. The keyboard feels quite satisfying, although it does require more push than it does on my Nokia, it's a 4 row (a bonus compared to my Nokia's 3 row keyboard ) The threaded SMS is beautiful!
The screen is big and great, it does have Gorilla Glass display (as confirmed on GSM Arena ), practically speaking, it is unscratchable, unshatterable, completely withstanding type of glass used as a protective window.
The feel and build quality is outstanding, a rubber matte feel and aluminium casing all around, I love the fact it has a dedicated sliding button to release the aluminium battery cover, making it easy to either switch batteries and memory cards from time to time. This also prevents the metal cover from being bent by accident, although it is quite sturdy, and not thin and flimsy at all.
As for the battery usage, you can easily reduce battery usage. Do the following:
Go into "Settings" and "Wireless & networks" then scroll down and untick the "Mobile network". Job done.
Doing so would stop any apps from accessing the internet in the background or foreground regardless of what you're doing. Also put your brightness to automatically adjusted. this will help too.
There's also convenient HTC widget for toggling this as well as your other wireless connections (i.e WiFi, Bluetooth, etc.), you will find this through "Widgets" then "Settings" then "Network dashboard" something along those lines.
Presto! You can instantly allow constant internet connection in just as few as two presses! (Providing that you've put the widget in main homescreen)
As far as the hinge goes, I have not had any problems or issues with it. I'll admit the hinge is quite weak compared to my N97 mini, but nonetheless the hinge is still strong and not breakable unless you do something out of the ordinary.
The optical trackpad is an added convenience, it does come in handy at times, but isn't used on a daily basis. It does help to correctly select a link without having to zoom-in completely.
The camera of this phone is probably one of it's downfalls when compared to my N97 mini's camera, pictures aren't always sharp or clear, the slightest shake or movement while hitting the shutter button will completely distort the image. Hence I would have to re-take some photos before seeing any good results. With my Nokia it was simply a matter of having the correct distance for the autofocus to work then press the shutter button, it would give me a perfectly clear, vibrant and sharp image. Apparently the Desire Z loses in this case.
One of my main reasons for buying this is the HTCSense.com facility to backup, remotely wipe data, track and locate, call it from a silent profile to a loud one. This doesn't work out of the box, you have to register and also allow this feature on your phone.
As for parents of teens, this track and locate feature would come in handy, as long as your teen does not know about this feature and then deactivates it from the phone.
Overall having this phone as my 19th B'Day present was great for me, despite dual-core phones are coming out, I have rooted my phone and overclocked it (it can go from 800MHz to 1.4GHz!), this is so it can keep up with future higher power demand from apps and other uses to come in the two years I have this phone for. I'm on 24 month contract.