I'm using the Lapdock Atrix, but yeah, same thing as the 500 basically. I really think Lapdock+PC-On-Stick is my new direction, away from the Apple Hegemony. It is simply amazing being able to carry my Ubuntu workstation with me in my pocket, plug into big screen/&etc., or use the lapdock on train rides (typical laptop use case for me personally) to do extra work. Its truly neat. I hope it happens mainstream..
As long as things keep going multi-core, ARM is going to be just fine for me. x86 compatability not such a need.. We've got Linode for that. ;)
Most PC-on-Sticks' use HDMI video output. I have a small dodgy cable rig to go from HDMI out to Lapdock HDMI in, but thats just because: Motorola. It could be quite feasible that Lapdock clones will arrive soon, with standard connectors..