The only social stigma comes from outside your own peer-group. All of my friends ride; and anytime we meet up no matter where, everybody arrives on bikes. London's not the best place to own a car anyway, unless you're prepared to put up with constant parking tickets and £5 per day congestion charge. The reward comes every night on the way home when you ride past the solid lines of lucky car owners who all wish they'd come in by bike today.