I recently picked up a Samsung Blackjack from Cingular and have to say that I love it! I've been a Windows CE junkie for years (I even wrote my Masters Thesis on an original Casiopeia A-11 HPC), so I'm biased of course. Switching from the Pocket PC OS to the Smartphone OS has been interesting, but I adapted fairly quickly. Complaints I'd read about the battery life on the Blackjack don't seem to be an issue now that they ship an extended battery (and a standard battery) with all Blackjacks.
Before I switched away from my Pocket PC, I was using Kevin Daly's excellent blogging app, Diarist. It doesn't support Smartphones though. Anyone know of a decent blogging app for WM5 smartphones?