I've just added a 4th bag to my collection, so I found this thread and thought I'd go ahead and list all of my bags and their uses.
1. Kata R102 backpack - this is the big travel bag that holds everything...it is for transport, travel, and home storage, but not much in-the-field use as it is quite heavy with everything in it. Currently holding DSLR body and 7 lenses, flash, and all wires, chargers, batteries, filters, cleaning kit, and remotes (also P&S camera and accessories, and netbook with charger when traveling). It acts as a home base, either from home or at hotels/villas/ship cabins etc.
2. Tenba Shootout shoulder bag - this one gets used when I'm out in the field and want to bring camera plus 3 lenses, or two lenses and flash. The bag can comfortably handle the camera with 18-250mm zoom attached, and bring along two smallish lenses, such as my 50mm F1.7, 30mm F1.4, 10-24mm UWA, or 90mm F2.8 macro. The camera can lay inside for rain protection or storage, but mostly the camera is out and the bag is there for carrying a few extra lenses and as a rain shelter.
3. Tamrac Adventure video bag - No, I don't use it for video - I actually use it as a soft, emergency DSLR bag. I'll bring this one when I want to travel light, with mainly just my camera and one mounted lens...the bag is often empty and just there to serve as a rain or splash shelter for the camera if I get caught out...sometimes I'll bring a small prime like the 50mm F1.7 along in the bag - and can just wedge the DSLR with attached lens + the 50mm in the bag with the zipper closed.
4. Think Tank Retrospective Lens Changer 2 - My most recent bag, just purchased and due to arrive in a few days! This one is a dream bag that I've been on the hunt for as long as I've had DSLRs...the one thing NONE of my bags could do was allow me to have access to my two long tele lenses, with the ability to change between them on the fly without putting anything down. I currently do a lot of bird and wildlife photography, and shoot with a Tamron 200-500mm lens as well as a Minolta 300mm F4 prime. Both lenses are about 8.5" long, and both about 4 - 4.5" wide...so few bags can accomodate either one in the first place. Those that do, require opening the bag, unmounting the attached long lens from the camera, putting it down somewhere, removing the other long lens from the bag, uncapping it, attaching it to the camera, then capping and putting away the other long lens - usually they share the same slot. It's an unwieldy operation to have to do...made more complex when doing it in a wetlands, forest, or dirt levee. What I love about this bag is that it is designed holster-style, or vertically oriented for long lenses...it has two side-by-side lens pouches with a flexible flap that lays over the top. The mounts of the lenses face up and out...the bag isn't designed to carry the DSLR attached. When you're a two long-lens shooter, it's the ability to switch between them easily on the fly that's the big selling point. Say I've got my Tamron 200-500 mounted to my DSLR...and I've got the 300mm F4 in one of the two lens slots (the other is empty)...the bag hangs low off the shoulder, either cross shoulder or straight...I'd adjust it long, to hip height. If I want to change lenses, I flip the lid up, insert the Tamron 200-500 into the empty chamber, and hit the lens release...off comes the DSLR, and the lens is in the empty chamber...swap lens caps from one to the other, then twist-on the DSLR body to the 300mm lens which is sticking mount up...once locked, pull it out of the sheath, and you've just switched lenses without putting anything down on the ground or fumbling with balance. What a nifty idea!
I had actually been proposing around the photo forums for over a year looking for exactly this solution - mentioning I had two long lenses and wanted a long holster type bag that could let me switch between the two on the fly - noone had one, or knew what I was looking for. Finally, someone on a photo forum mentioned that these Think Tank bags sounded a lot like what I was looking for...following the link, I knew that I had ended my search. I contacted Think Tank on one issue - the specs say the bag can handle two lenses up to 70-200 F2.8 in size...both of my lenses exceed the typical dimensions of that lens. But after talking with a rep, they measured out a lens of 4.5" diameter and up to about 10" long can fit in each pocket. The top flap is flexible and soft and can accomodate lenses sticking out of the two pockets a bit...as it happens mine are about 8.5", so they'll fit comfortably in the 9" space.
So that'll round out my bag collection at least for a little while!
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 150-600mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony A6000 / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / 10-18mm F4 / 35mm F1.8 / 16mm F2.8 / via manual adapter, lots of Pentax K mount, Konica K/AR mount, and Leica M mount manual lenses