What Happens If An Astronaut Floats Off In Space?

NASA requires spacewalking astronauts to use tethers (and sometimes additional anchors). But should those fail, you'd float off according to whatever forces were acting on you when you broke loose. You'd definitely be weightless. You'd possibly be spinning.

In the film Gravity, which opens this month, two astronauts are on a spacewalk when an accident hurtles them into the void. So what would actually happen if you went, in NASA's terminology, 'overboard?'