O.K., I probably won't check this bag when I travel, but I think that it will be a good bag to travel with.
Yes, after all of my complaints I've finished the Amy Butler High Street Messenger Bag--it's been weeks since I pulled it out, but I spent four or five hours on it today and now it's done. The exterior fabric is an Amy Butler design as well, and the lining is a super cheap dark denim. Given that I normally wear pretty neutral colors, it's not likely to clash with my clothes, but the bag is very large and very bright. I think that it might look better with a little more of the denim on the exterior, or at least underneath the front flap.
This is certainly the most complicated bag pattern I've made, and overall I think that it came out very well. If I had more patience, the bag would be more perfect, but I fully expect that it will be very durable and useful. There is a "tool organizer" on the inside (see right), and a total of three zippered pockets, as well as two pockets underneath the front flap. The downside of all of the pockets, and the size of the bag, is that the bag weighs a ton empty, and once it's full of crap it will weigh three tons. The strap is a little short for me, but should be fine if the bag isn't stuffed too full. Given the amount of slightly annoying detail in the pattern (I must have been reminded maybe 25 times to backstitch at the beginning and end of a seam), I'm surprised that there was no option to fit the strap to the sewer. Also, at times I was sewing through a ton of layers, and although my machine has a powerful motor (it's a Bernina) it wasn't easy. I don't think that any of my previous, more "standard" machines would have been able to make this bag.
I haven't surfed around too much to see if others have had similar problems making this bag, but I'm definitely not sorry that I made it. I'd be surprised if I make another one of these, but it's given me some good design / construction ideas for some smaller bags.