I don't have a carpc, but I do have a 7" touchscreen hooked to my laptop.
I run Centrafuse front-end software, which pretty much controls everything. It plays my mp3's, my XM radio (XMpcr) and *can* do my phone though bluetooth, but I prefer my headset for that.
For navigation, I use
Garmin MobilePC. There's a plugin for Centrafuse (actually there's 2 of them available). I use the
BU-353 receiver and love it. I had issues awhile back with it, but it turns out that it was my CB causing the problem. That's been solved.
So far, it's worked out REALLY good for me. I've got an HP slimline computer that I'm going to swap out the hard drive (put in a laptop drive) so that I can mount a 21" monitor in the sleeper of the truck for use when I'm parked.