I have the Frank Dog bag. It will fit a 15" laptop in a padded sleeve. It is a pretty nice bag, but there are definitely improvements that could be made. Jensen has them really cheap, but in some pretty horrendous colors. The two improvements that I've considered would be a shock strap to hold it against the rack, right now it just hangs, and more useful pockets, both internal and external. I want to be able to zip my keys up somewhere easily accessible and the only zipper pocket is shallow and tight between the laptop and the back. The laptop pocket itself is very nice, with a velcro enclosure and ample padding. I also find the shoulder strap to come off too easily.

The one review I read is that it does hang too low and will drag against the brake and wheel when used as a handlebar bag. They have other bags that may fit better, but I would look at different systems as well if I'm going to start over with a new bag.