Having read a few messages since my time with Camel travel I thought I'd just add a few more words, there is the old addage that you get what you pay for (I paid $35), but Camel just have no respect for their clients. I have traveled from Hanoi to HCMC with Camel on their sleeper buses stopping off at various points along the way. Be prepared for a combination of the following in my expereience;
Shouting from drivers and their co-drivers
Smoking drivers on a no smoking bus
Toilets out of order
Poor quality 'beds' that fail to recline
Locals sleeping in the ailes
Your luggage to get wet whilst in the hold
Rain water to come through the bus to your sleeping area
Distinct lack of leg room (although I am 6'2")
Bugs in and around the inside of the bus
With regards to the taking off of shoes, it is courtusy to take your shoes off when going in to a Vietnamese house so I gathered it was a similar thing with regards to getting on the bus.
But at the end of the day I took the tour from opposite my hostel as it was cheap, convient and got me to my destination , but it doesn't harm to do some research, I would just say find someone else and they can't be half as bad.