jpatokal, I've been meaning to ask:
--what's the going rate for the tuktuk from the Thai-Lao border up to Vientiane?
Posted price is 150 baht for your own tuktuk, but since everybody's going to Vientiane, most people share (they'll drop you off directly at your hotel). That price is negotiable if you're there at a quiet time.
--did you somehow get a chance to get GPS coordinates of the termnation of the Lao train going toward Vientiane?
No, because the shuttle was cancelled the day I was there.