Depending on where I'm going and what for, I sometimes load up a Duluth Trading Company Presentation Jacket - which also has lots of pockets - when the gear I'd normally carry some other way. The body's cut a little large for my 50" chest / 36" waist, and with all that crap in the pockets it drapes pretty well. I don't substitute it for my BOB but it's pretty handy when I'm carrying a handgun and other supplies along with some basic gear.
Downsides
1 - most jackets aren't built heavy enough to handle a constant full load, and you may find yourself walking around looking like the Michelin Tire Man.
2 - "Now which pocket did I put my snakebite kit in?"
3 - It's not a great summer option in KS, but sometimes it's the only thing that fits the bill.
Upsides
1 - your stuff is with you
2 - you don't have to lug a separate bag around
3 - It's an option that works better than anything else - SOMETIMES.
Neutral
I haven't tried flying with one yet. I'm curious/apprehensive about the reaction one would get from the TSA folks. I suppose as long as there's nothing in the pockets that's prohibited they'd just have a good time exploring all the stuff inside them, eh?
I haven't seen the Travelsmith catalog - what's the material used for the jacket? I'd like to see one made of heavy canvas, but I haven't come across a resonably priced example of that.