Yep! I do, and it works great.
I have it in a heavily modified otterbox 2000 with soft plastic window. This box was actually made as a prototype only, but worked so well that it is still on. There is mainly a few cosmetic issues.
I have rigged it with external antenna, power in and audio out and mounted it with a RAM-mount.
My brother and I just made a 4000 km trip on the continent without any probs. He is using a SP III, and I wouldn't trade with him.
The only drawback is that the Ique screen is not bright enough. On very sunny days, wearing sunglasses the display might be hard to read.
The big advantage over the SPIII (except for supplying you with additional mp3 music, e-books, e-mail and games on your trip) is the speed when finding places, calculating & recalculating routes. The SP III is much slower.
Another big advantage is the use of standard commercial MMC memory cards. I believe that there are up to 2GB available today (?).
What I really would need now is some small program that can flip the screen to horizontal. That would give me back the view of the speedo (need it for sunny days)
/JOP