cheaper and better than the HP Touchpad keyboard since it works well with PB and iDevices, PLUS it's a standard keyboard with ESC, Alt, F1, F2, F3...buttons, etc...
I just picked one up (using it to type this). I'm not sure how often I will use it (or have it with me when I'm running around), but for $20, I figured why not grab one?
It's nice to have actual cursor control (arrow keys). It sure makes editing messages so much easier! There's sometimes lag between typing and the text coming up on screen, but I am a two-finger "hunt and peck" typist, so I don't think it will be a problem for me.