Went for a twenty or so mile ride today with the Seagull black bag. This is my same school load, which doesn't even put a dent in the bag's capacity. The only time the bag moved was when I started bouncing from spinning the pedals too fast [~120 RPM or so...I am still a n00b to cycling for the most part], and even then it was because I was bouncing a little bit. The bag is far more comfortable in the drops than the Timbuk2.

I like the fact that the Timbuk2 is more organized, and it pretty well designed as far as carrying pencils, notebooks, small things, etc. I picked up a few organizational pockets from REI, and I am going to use them to keep the Seagull straightened out.

There really is no comparison between the two bags. The Seagull is a messenger bag; the Timbuk2 isn't. Great bag for wearing over the shoulder and walking around in, but not great on a bike. OK, but not great.

Two questions about the Seagull Black Bag: has anyone broken one, and what the heck will happen if I take a spill and land on my chest with that giant buckle there? Chrome is the same way, I think.