How much benefit can one expect from a monopod?

I find I get about 1 stop more by using a monopod. Maybe 2 stops, if I'm lucky.

Functionally, it's pretty much the same as hand-holding, only a bit less shaky because the camera only has two degrees of freedom instead of three. So you can still make use of image stabilisation. Camera weight shouldn't be an issue, since the monopod won't be supporting the whole weight of the equipment anyway.

Obviously, a monopod won't do for really long exposures, nor for anything that relies on having the exact same camera position from one shot to the next.

On the plus side: you can often get away with a monopod in places like museums that don't allow tripods.

One thing you may want to look for in a monopod is one that can become self standing. They're not as stable as a proper tripod, but under the right circumstances they can really help in getting some shots. Manfrotto makes one and there are others kicking around as well.

I've got a Trekpod - a monopod with fold-out tripod legs on the bottom. It's slightly heavier than a "plain" monopod, but quite a bit more versatile. One of the issues you'd potentially run into is stability, since the "legs" are relatively short (around 14", I'd estimate). If you consider it to be a monopod with the additional stability of these legs, though (and not as a true tripod), it ends up being pretty handy.

I've had decent luck using the Trekpod with a Panasonic FZ-28, which is lighter than your setup. Placement is important, since it's naturally going to be top-heavy, and the platform is susceptible to swaying if there's more than a light breeze. You can improve stability somewhat by leaving the pole collapsed to walking-stick height (rather than extended to near-eye level).

All these disclosures aside, I've been able to use the Trekpod for long-exposure shots more often than not, and I was happy to have it with me as a walking stick on a trip to Canada earlier this summer. For me, the fact that it does double duty outweighs the shortcomings of the hybrid design.

I've been using a monopod for over fours years now, predominantly in situations where I'm treking through rough terrain and a tripod would take too much time to set up and break down. I've found it particularly useful in shooting wildlife (penguin colonies for instance) where I'm often moving position very frequently.

It's also been invaluable for shooting from non-stable platforms - in my case the decks of ships at sea, where a tripod would provide no stability whatsoever.

Where I use my mono-pod is video. Taking the video camera to school functions, where you are packed in small seats means a tripod is out of the question. Holding a video camera up to your eye for a 45 minute performance is asking for a sore arm, and sore eyes. I find that the mono-pod will fit in the space between me and the person in front of me, and with an LCD on the video-cam, I can move my eye away from the viewfinder, and actually watch the show. Plus I can place the camera a little to the side, or above the head of the person in front if I don't have a good line of sight. It does make a decent walking stick as well.

I tried one for a very short time and got frustrated from not gaining significant stabilization for my needs, so I returned it. However, this may be a problem with my undeveloped technique and lack of practice with monos.

One thing that it can be useful for, though, is as an available solution for ad-hoc leveling of your camera, in case the horizon is problematic. You need to hang the monopod from the camera, rather than rest the camera on the mono. This way, its weight will give you perfect leveling.

I am using very basic monopod Velbon UP 4DX II 4 Section Unipod and I am satisfied for the price. It is very useful when I shoot with my Tamron 70-300 - the focusing is much easier and also waiting for optimal shot is better as you do not have to hold the camera with long telephoto lens only in your hands.

In some cases - as already mentioned - museums, street, crowds of people - it is not possible to use tripod, because it is forbidden or it is a risk for your camera.

I also though about the combination of trekking pole and monopod and many people suggested not to do it as trekking pole needs to be very tough and it is not constructed to often and quickly change its height. On the other side, the monopod does not have to be able to carry about 80 kilograms like the trekking pole and it must be constructed to be quickly released and packed again.

Situations for which I find a monopod useful:

1. When shooting an event for several hours, allowing the monopod to support the weight of a heavy lens is quite beneficial for your arm, shoulder, neck, and back muscles.

2. You can "stack" the benefits of IS and the extra stabilization the monopod supplies. If you're using a 200mm lens on a 1.6x crop body, you would normally need a shutter speed (Tv) of around 1/320 sec. With four stop IS you can drop the Tv to around 1/20 sec. Put it on a monopod and with good techniques you can go to 1/10 or even 1/5 sec! Of course that is assuming your subject is not moving.

3. If your subject is in motion horizontally, like a race car for instance, you can pan on the one axis while the monopod allows very little up/down motion of the camera. Combined with Canon's mode 2 IS, you can really keep your main subject sharp while everything around it is blurred along the direction of your subject's motion.

4. Even though it only has 1/3 as many legs, I find my monopod provides a much more appreciable benefit than 1/3 of that gained by my tripod. And that benefit can be enjoyed in locations where tripods are not allowed.