The sewn-in laptop sleeve on a Timbuk2 medium takes up about 2" of internal space. It did however, provide some structur to the back, and flash and small lens or two could fit in there when not toting the laptop. The funny thing about the sleeve is that they only sew it on the top, and the sides and bottom use Velcro to hold it in place. The Domke inserts I had simply took up too much space. A 40D with my smallest lens--30mm f/1.4, is NOT a small camera, especially when a grip is added. Another note--the Crumpler 7MDH is actually smaller than a Timbuk2 medium laptop messenger bag. It is beyond me how people really carry as much stuff in the 7MDH that they claim--the padding in the 7MDH takes up a lot of interior room. I still have not given up on the Timbuk2 messenger bag plan--I need to make my own interior dividers and simply NOT try to carry much stuff in the bag. Right now for stealth, I use my CC Filson medium field bag with a towel tossed in for padding, and carry my 40D with 18-200 OS, a flash, some batteries, Epson P-2000, and some other odds and ends, and sometimes my 30mm f/1.4 in a sock. My camera stuff actually fits in this bag better than in the Timbuck2 I had as the heavy waxed/oiled canvas and bridle leather of the Filson bag has more structur than the Timbuk2 back, not to mention looks more classy and rugged. I will also say that when I added a computer and charging cord to the Timbuk2 bag, along with the camera stuff mentioned above--it was way too much to carry comfortably--and I am not a small person.
The moral of the story is that we need more than one way to carry camera stuff to fit the purpose of the outing, and we need to make choices on what to bring when we venture forth with camera gear. There is no one "perfect" camera bag--that bag would be the size of my wallet, fit in my other back pocket, and hold about a 1/4 of the Canon lenses, a couple of flashes and bodies, weigh under a half pound, and open and close itself with the press of a button!