I have played around with Blackberry handsets, before, namely the Bold 9000. My opinion at the time was that while it was a good device, it wouldn't be my primary device. And I stick by that assertion.
As a second (or backup) device however, its unbeatable. As a result, I've enjoyed the stability, responsiveness and absolute solid call quality of the device so much, that when I had to return my loan device, I needed a replacement. The Curve 8520 is being flogged by all the operators in South Africa, so I took the plunge and bought one. Its great! Same structure and featureset as its bigger and more expensive brother, but without a GPS, a feature I can live without.
A nice device! And even nicer when you hack OS 5 onto it.