Another Treo user chiming in here. Actually, I've switched to the Centro, but it's really the same difference. The Treo is probably a better choice for sheer productivity, due to the better keyboard and vastly superior battery life. Personally, I'm not a fan of Windows Mobile's menu-driven interface, but after testing the 800w, I'm considering switching, and adding a
Celio Redfly for netbook functionality.
If you go with the Palm, you might want to take a look of my GTD configuration instructions in my post,
How to Set up GTD on a Palm.