I live in manhattan and couldnt see myself buying any bike more expensive than my kilo. And even then Im super paranoid, I lock up with a 15lb fahgettaboudit chain for frame and rear and evo mini lock for the front wheel. I try not to leave it locked outside for more than a couple hours, and never during nighttime. There are a few perks that come with this though, when I take off my backpack full of locks and books to joyride I feel like a rocket.

Oh and something that might be useful that I conjured to avoid parts being stolen. I take bits of tin foil and shove them tightly into allen bolts to avoid people from unscrewing things. If you do it well enough and really compact/flatten the aluminum it also looks as though the bolts have been completely welded or soldered, and its impossible to stick an allen wrench in. When I need to readjust or replace stuff I just take a knife and slowly/carefully ease the foil out.