Nice video. I hadn't seen the smaller version of the plug yet. Cool.
I actually do have a 3G connection on my plug. It's a verizon USB stick. I got it working with wvdial after some serious screwing. Works great. Only issue is that verizon drops an idle connection after 5 minutes, so I just wrote a script to have it ping google every 4 minutes. I also wrote another to make sure the connection restarts if it is lost.
I setup a wifi access point in my car by hooking a linksys "router" into the sheeva's ethernet port and turning off the DHCP and routing servers on the router. Then I setup the plug as a DHCP server, DNS server, and a gateway.