I've had two companies that switched technology between recruiting me and the start of my employment. It was a bit irritating, but provided an interesting way to learn something new on someone else's dime.

I've also been at a place where I was not allowed to program in C, but had to do all the code reviews for the people programming in C. The "logic" was that since I was doing the code reviews, I shouldn't program in C since no one would review my code. I sometimes wonder about how I encounter these situations a bit too often.