We crossed on the 16th Dec 2013. One UK plate and one US plate. After the visa queue etc a guard came over said he need passports and bike docs and said he needed to photocopy them.. which he did. We met a couple of Malaysian bikers who told us they were refused entry but they were gone ride in anyway. They had parked their bikes up behind the visa portacabin in a dedicated are not sure why... Anyway the guard then told us to go to customs, which is sort of in the town. Hopped on bike rode to customs..parked up, walked in and got told we weren't allowed entry as we needed some letter from the Cambodian something authority. So then we tried to explain overlanding etc etc.. the dude called his boss, then he said no but then we staretd again, they asked us how we went through other countries so showed them stamps of vehicles etc in our passports (didn't show them the carnet as they didnt ask for it or didnt know what it was, I did mention it however). So they said they didn't know what to do, we said can we purchase this document how do we get hold of it they said no. They said they had no authority to stamp anything etc etc. We argued that they had to stamp and sign SOMETHING so in the end we convinced them to stamp a photocopy of the vehicle registration documents. Probably worthless but better than nothing. At no point did ANYONE ask for or imply a bribe. It apperaed all normal. Apart from the visa guy who asked everyone he could jump the queue for them but thats irrelevant.
Also, I met a traveller coming the other way, and he said the guy at the Laos border (Cambodian side) knew wha do to and stamped his Carnet etc. Hope he can get it stamped out.
Also if you any of the Malaysia dudes is reading this, let us know how you got on?
P.S. Once you get your visa and passport stamped there is nothing stopping you to ride in, there are no further checkpoits etc. You just get told you're not allowed in.. When exiting into Laos, I am just going to ignore customs and just exit Cambodia.
All the best,
Oli