I've been screwing around with the Targus ThumbPad for my Palm M505. Eventhough I'm pretty comfortable with Graffiti, these "thumboard" thingies seem to be the next wave, as they are showing up on Treos and Palm is threating to put them into the next version of PDA.
The odd thing I noticed: once you put yourself in the keyboard frame of mind, you expect certain things, like an ESC key or a DEL key that is easily discernable. I also found myself expecting Emacs-style cursor movement.
So, first of all, the application has to know what do to with Ctrl keys or the ESC, and naturally next to nothing on the Palm does (except the Pedit suite). Secondly, the DEL key is under the P and is the same shape. They (or rather the OEM they relabled it from) strived for a pretty symetrical look to the keyboard. Heck, just give the DEL key a different color and that'll help a lot.
Anyway, I recommend installing LapTopHack. It really makes the keyboard useful.
Since I can't really whip out the laptop on the various public transportation modes I take, this allows me do some serious typing while crammed between a fat smelly guy on the left and the uptight suit on the right reading the latest business managent book.
