So, what exactly are these guys?

I mean--I know what they look like...

But what exactly do they do?

Wikipedia didn't help me, so I thought I'd ask some relative intelligent people for an answer.

Oh yeah--and what are the locks on some guitars on the nuts? What are those called and what exactly do they do?

More importantly should I get some for my guitar
Floyd Rose Tremolo and Locking nut.
They are put on the guitar so you can go crazy with teh whammy bar without it going out of tune
They were Designed in the 70' i Beleive, by a Man Named Floyd Rose. Leo Fender invented the first Tremolo Unit, which was non Floating. It had a lot of tuning issues, so Floyd created ones that Floated in the body of the guitar, alowing them to be pulled up further, and pushed down more than the standard Tremolo type. these had even bigger tuning issues, so he Locked the strings in place on the bridge, and at the nut. This is the locking Nut. It was First brought into the public Eye but a guitarist you may know, he was in a Pretty small band. had a few hits. Name was Eddie.

im 99% sure thats how it works.