I lived in Boston from 97 to 02 and never really thought about bike security. You'd see tons of messengers frame locking and leaning their bikes against the wall of a building, you never really saw seats locked on with an old chain and old tube. Hell, I once managed to lock only the front wheel and not the frame. It was a quick release wheel and everything was still there six hours later.
Now that I live in NYC, I lock everything. When I'm out, I use an thin krypto cable through the seatpost rails locked on with this tiny U lock I got at Continuum Cyles (Avenue B between 12 and 13th Streets - check it out). That lock also locks my rear wheel to the seat stay. I then used the extended Krypto Evo (all I ever used in Boston) lock through the front wheel, frame, and post. At work, while locked up in front of a big window, I use an NYC chain to lock through rear wheel and frame to the bike rack and hook the actual lock through the seat rail so I get that in there too. Since I have the other locks with me, I just use them as I normally do. I just leave the chain locked to the bike rack.
I'm kinda serious about bike security.