I wouldn't usually have any qualms about locking up an expensive bike under those circumstances. It's schools that get a lot of bike thefts, because of the massive congregations of bikes. I've learned the hard way. There are some precautions. I like to have a quick release on the seat post, so I just take it in with me, and I don't want a quick release wheel. Or if I do have them, then I'll take off the front heel, and lock it to the frame and back wheel. Nothing is completely secure, but for a shortish period of time, you should be okay. I'm also a big fan of the uglification factor. Thiefs tend to be attracted to aluminum frames over steel (bigger, newer looking) and carbon looks good too, naturally. Some well placed mud, racks, and stickers can help draw attention away from the bike and towards some shinier models, perhaps.

Then again, did any Portlanders read this article in the Willamette Week?

http://www.wweek.com/editorial/3242/7923

It's a bit disturbing (I'm sure it's been posted on these boards before, gimme a break, I'm new here