My son just got some for his bday. They're pretty cool and the best part is that his little sister can't lose the tops of the markers and they won't dry out.
DD has some (we have a white board portion on her easel). You have to scrub pretty hard to erase them. . . that's my only complaint. She can't do it herself, so I'm forever erasing for her.
Re: Dry erase crayons?