Summary: Having accumulated quite a few bags, this is my favorite shoulder/waist bag. The supposed "lens bags" on the sides, though are just large enough (diameter) to accommodate a Canon 580EX flash... not any lens I own. I replaced them with the proper Lowepro lens bags and it's a great setup.
Pros: Comfortable Strap, Good Protection, Lightweight, Lots Of Pockets And Features
Summary: I wanted a shoulder bag to hold my Canon 30D, a few lenses and a flash. At present I carry my 30D with a 24-105 F4L (with hood) and 70-300 F4/5.6 IS in the main compartment and normally a 420EX flash with Stoffen Omnibounce fitted in one poucha nd a Tamron 90mm in the other. The pouches fit these lense fine, but a 70-200 F2.8 L or 100-400 F4.5/5.6 L would be too large (although you could get a bigger slip-lock pouch).
Pros: Can wear over shoulder or around waist comfortable, can add or remove pouches, useful pockets for filters etc. can access equipment quickly.
Cons: Not enough room for large telephoto lenses, no waterproof cover, padded belt is bulky when packed away (can't be removed)