A friend of mine does something like this to test the waters. This approach seems to help prepare to be prepared. But then he sometimes has to face the dilemma- whether to accept the next opportunity. :-)
I can't imagine doing this without actively thinking about leaving my current job for whatever company I'm interviewing with.
Which is maybe not a bad idea, say once or twice a year? Even a loyal and supportive manager has certainly run the numbers on life with or without you on the team, and will be told to do so again at some point.
