Good vs Bad Outsourcing

The company I work for is planning to outsource at least a part of the whole IT department, full scope undecided. Workforce blissfully kept in the dark as much as possible. Frustration running high and expecting to see the rats abandon ship.

What are the different experiences with outsourcing? The good, the bad and the ugly? Have you seen a lemon, good experiences everything is interesting. Just wanted to know!