what's the catch?
Call me paranoid, but I note they're using version 2 of the GPL, not version 3 which protects people from submarine patents. So they get this stuff to infect non-Microsoft code, then turn around and start suing people. That's a very Microsoft move right there.
Embrace, Extend, Extinguish. It worked in the 80's. It worked in the 90's. I'm guessing it will work for them in this decade as well, and people will just keep helping them make it work by being trusting fools.
Beware the beast, he is the devil
Who grabs your hand and leads you in
Beware the beast, he is in revel
He guides you to fire