According to this post on the Lonely Planet Thorntree, the much anticipated coastal border crossing between Cambodia and Vietnam is now officially open for foreigners.
The crossing, close to Kep in Cambodia and Ha Tien in Vietnam, will allow travellers to head from Ko Chang in Thailand to Phu Quoc in Vietnam without passing through central Cambodia.
According to the report, neither Cambodian, nor Vietnamese visas are available at the crossing. You must have your visa beforehand.
The poster goes on to say:
"I talked to four different people and was quoted US$5-$15 for a motodop and $10-$25 for a tuk-tuk. The real price will probably settle around $8-$10 for a motodop and $15 or more for a tuk tuk.
There is not much at the crossing point. Checkpoint shacks and the new immigration building. No foreigner services. No obvious waiting onward transportation.
A guy in a coffee shop on the Cambodian side of the border told me that once you are on the Vietnamese side, a motodop to Ha Tien costs about $2-$3 and to Ba Hon a bit more. He said you can catch a boat to Phu Quoc from either town but that Ba Hon was better."
So there you have it!