It's usually cash. They do it so that you'll actually spend it and be happy instead of just depositing it into your bank. Googler friends of mine say it happens every year a few weeks before christmas. This instance was unusual because the cash was given out so early.

A friend of mine also recalls a team who stuffs envelopes full of cash -- it's a lot of work stuffing 10,000 envelopes (this was for the MV offices)