Another feature I appreciate is the inclusion of Pocket Office. The files integrate perfectly Office programs on my computer. Pocket Word has been incredibly useful. Paragraph and document formating is preserved, saving lots of time. This much more useful than the notepad program on palm-sized units.
Screen size is another consideration.
With almost twice the viewing area, handhelds like the 810C offer an environment closer to your that of your desktop computer. Programs offered in Pocket Office just wouldn't be as effective with less visable real-estate. The pcmcia slot allows for a multitude of expansion options. I presently have a SanDisk Compact Flash PC Card Adapter for my 16MB CF occupying the slot. There is even a built-in modem.