Dogs hate them, and the bed usually ends up bundled in a corner after the dog has had a total hissy fit getting into the kennel due to it beiong slippery.
Use rubber car mats to stop the beds slipping, the dogs walk in no problems and no stress, and they are easily washed too.
We use thick rubber mats in our larger dog kennels and find them great. The only downfall we find is the odd naughty dog will chew on then so obviously remove before chewers are placed in kennel :-)