This post is very similar to the HTC Desire HD hands-on post. This happens when HTC decides to announce two really cool devices on the same day. The hands-on pics are and videos are from different people.
It looks like the Desire HD is meant as a media consumption device and the Desire Z is more of a business device. This would be like the N and C series in Nokia (was that a dated reference?). At any rate, the Desire Z has a fantastic keyboard and spacious 3.7 inch screen.
One thing we have come to love from HTC's high-end devices is how sturdy the construction is. There is no change with the Desire Z. There are some concerns with that new "Z hinge," as it seems likely to break quickly. That said though, that hinge opens up on a great keyboard, with just the right amount of clickiness and travel.
The new version of Sense has a few cool features, including the ability to change the order of your homescreens using the expos©-like helicopter view. Some other tweaks include easier to use widgets, and a car-mode that is more intuitive. Further, you can log in to htcsense.com, and find your lost phone, text or call it, or even wipe the data remotely. You can also browse your text message history, upload media to the site and it will link with your phone, and you can preload the phone with map data using HTC Locations so that you don't need to pull down maps from the network while you are on the go.
All in all, it looks to be a pretty good device. Look for a review after it's been handled for a while.
Below we have some hands-on pics and video of the Desire Z in action, thanks to Slashgear.