I just got my hands on one of these devices and I have to admit I really like it!
I tend to carry a number of devices in different categories for demos and customer meetings.
Yesterday the O2 XDA Orbit became my official Pocket PC SatNav device. I loaded up ALK Co-Pilot and it worked flawlessly on the device. I used it to navigate my way to the office today (yes I do know the route but it was my first journey since getting it)
I used to use the Mitac MIO A701 device for SatNav but the XDA Orbit is feels slightly smaller even though physically it's a very similar size.
The dial navigation and trackball takes a bit of getting used to but I haven't been put off by it. A few applications behave slightly differently with it though which takes a little patience.
It's frustrating that the FM Radio only works with the supplied headphones... I need to get one of the ExtUSB dongles to see if that will work with another set of headphones.
Overall though a great device!!!
Cnet have also just published a more indepth review HERE