The first one that popped in to my mind, was when Jarrett laid down for Hogan at Bash At The Beach. Hogan was rebounding from the nWo, and Jarrett was the champion, and top heel of the company.
The entire show was based around the big match, and when it happened, we all nearly crapped ourselves. Hogan didn't have to do anything on-screen to turn heel, and all Jarrett had to do to turn face was lay down.
Vince Russo did all the work. Apparently Hogan was politicking to win the match, and Russo was sick of it. Hogan won the match, and was released from WCW. Jarrett lost the match, but was still the champion until a match later in the night against Booker T, where Booker won the title.
I don't think it happens often, because there's rarely a set up for it. There's not really a need for two guys to switch at the same time, and it can get sloppy if it isn't done right. I think the current story with Big Show and Edge was meant to have this effect, and it didn't work.