I now have the Curve 8900 through O2, having upgraded from a Pearl 8120. I like the separate keys for each letter, but it took me a while to work out how to move applications from their folders to the 'Menu' screen. I use the Memo Pad and Calculator quite a lot, so it's easier to access them from the Blackberry button, rather than digging down through menus. Installation of Facebook and Twitter was a doddle, and I've aslo managed to install Mobipocket - kewl!
I upgraded Desktop Manager to 184.108.40.206 with the disc that came with the phone. It syncs ok, but then it searches for updates and I get an error message about the Application Loader, and it asks me to submit an error report.
The Curve hasn't locked up yet like the Pearl used to do - which required a battery pull. All things considered, it's a very nice piece of kit. Next puchase - Bluetooth headphones.