The Cambodian/Vietnam border at Moc Bai.

On the Cambodian Immigration side it's about as friendly as it gets, but once through the Vietnam Gate (seen through the Cambodian Gate, in the pic), things pretty much drop off the "Cyclists Well Come!" scale.

However, as long as your papers are in order, you'll be sweet. Vietnamese officials love paperwork.

RE Mr Pumpy's last minute "I can't leave Cambodia" sentiment, who can blame him? Felix is just worried about getting into Saigon before sunset (which they didn't), but they did come back after a week.