I just installed the El Mariachi-specific Relevate Designs Frame Bag---the first production full frame bag specific for one bike. Its made specifically for Salsa Cycles (hence the dual logo on it), and available on order through your local bike shop (Thanks Greg, at Beehive Bikes!) I'll post a thorough review after I've used it a while, but my first impression is that its constructed well, yet still lighter weight than I would have guessed, and certainly lighter than an equivalent-volume backpack. Two zippers, one for the big compartment and a small phone/wallet/map compartment. The big compartment has a velcro divider that you can adjust the size of, or even collapse away completely. It stores plenty of stuff. I dropped my completely full 4-liter water bladder in it and there is still room for an all-day's-ride-worth of food, spare tube, tools, pump, and basically the contents of the soon-to-be-removed saddle bag that's pictured above.
The initial verdict: without even riding with it, I already know that long hot summer days will be much improved with 4 liters below deck and no sweaty backpack or awkward schlepping of extra water bottles in my jersey. And now getting food won't even require stopping to twirl around the backpack: Just reach down and get what you need.
The final verdict: I've ridden with the bag for about two months now. I do like that it caries copious amounts of water, particularly on hot days. But now that its chillier, I also stash a jacket in there. I also stash my wallet, keys, lunch, all my tools... I never ride with anything in my jersey pockets or a cumbersome and sweaty backpack. The bike rides no different. Everything seems well-balanced.
The only drawback is the zippers. In any item that is suspended taught in a frame like this, the tension, particularly when fully loaded will go onto the zippers. After only two months my zippers are not zipping like they should. I rub a little dry Ivory soap on them to get them lubed and working well enough, but the small zipper is broken permanently and the large zipper is not as smooth as it used to be. They work OK but they do not zip up properly anymore, but bulge a little. Be sure not to over load the thing, and when carrying heavy loads, be careful not to reef on the zippers too hard. I see the zippers as a design flaw. Why not put some compression straps on an flap to close up the thing?
Final grade: B-, the zippers are a dumb idea that threaten the longevity of an otherwise nice piece. Careful use will probably prevent problems, but when you are out in the backcountry, why risk having another thing go wrong? It needs to be redesigned with straps, not zippers.