It's a great option
I like the keyboard... more than I did a week ago, fer shure.
It takes some getting used to, but I think that's true of any phone/PDA physical keyboard... it's inherently a compromise. If it weren't, it would be a foot-and-a-half wide, and include a jog shuttle, numeric keypad, and a few spare USB ports, just like the Bella DV keyboard on my desktop machine.
When I started on the Palm Treo 700p, I hated the keyboard. By the time it died, I hated it too, but in-between, I liked it. The fact that you have your choice of physical and virtual on the DROID just rocks. If I need to enter a few letters, the virtual KBD is fine (also, try voice recognition if you haven't.. it rocks... just wish the input options were more consistent).
For anything long, or when I'd actually like to see what's on the screen, the physical keyboard can't be beat. I don't think I would have opted for a thickerer phone just to get a thicker keyboard... this one's fine. My main issue is that I hand a tendency to swipe the screen with spare fingers while using the keyboard.. sometimes moving focus away. At least it's still there running, as I left it.
There will definitely be a little of the whole muscle-memory thing, learning this keyboard versus other micro-keyboards. As a guitar player, I can attest to the fact I've learned input systems far more torturous. I don't see how else they could have keyboard and "thin" in the same unit.