Looking for a small bag for your SLR? Well I'd suggest a Nova 1 bag instead, as this will be too much for your uses.
Looking for a large bag for two or more SLRs? Well this bag is too small.
If you however have a SLR, 2-3 lenses and a flash, it's just right. I carry my Nikon D70s (with a battery grip attached), 18-70, 70-300VR, and 50mm lenses as well as a SB600 flash in this bag. Any of the three lenses can be attached, and the other two can go along for the ride. The flash cannot fit attached to the camera, but it fits when you disconnect it. I even can throw in the AC adapter, extra batteries, extra compact flash cards, and a memory reader. All of this fits with the top securely zipped shut. The whole setup is a rather large and heavy affair, but it works well as a carry on. It seals well, so it's very weatherproof as is, but there is a raincoat thats stowed in the bottom that covers it even better (I don't think I want to be in a rainstorm that necessitates that). The one thing that can be an issue is that this bag is too much if you're just taking a camera and one lens. I still have a Nova 1, which serves this function well, and the dividers that came with the Nova 1 came in handy, as this bags allotment was sufficient for most uses, but not mine.