I think the poster above said most of what I wanted to say! - We are in the 'don't make them share' camp as well...
Modeling behaviour is the first most important thing (for all things - not just sharing!) -and for me this includes not 'snatching' from a child either. There have been two cases where my son has snatched from another child but I feel that it would not help to teach him how to behave more appropriatly if I just 'snatched' the toy back from him (gentle pried from his hands, however you want to word it
- There are many here who might argue that no matter what, a snatched toy must be given back even if that means prying the toy out of their childs hands ... I think this action to a very small child can be rather confusing, you are doing just what you told them not to do as sharing is very complex to understand...and perhaps to them they were not 'snatching' at all in the first place, maybe they too were just removing a toy from a child who they felt should not have it?). This has never been a real issue with my son - after explaining that so and so was playing with that, we will have to wait our turn, perhaps we could play with something else during that time, would you like to give the toy back - my son has given the toy back and moved on and waited his turn...But I have looked after other children who do not so easily give up an item snatched (I find it no coincidence that 'share' is also often shouted at them and that items are often forcably removed from their hands - that sharing is still such an issue for them even at the age of 4+) - this is when I feel that focusing on the offended child is most important (without shaming the other child). I do not think this teaches the child who snatched that their actions were okay at all - it instead can teach them not to snatch through natural concequences (oh - im not getting attention, even negative, for this...and so and so really doesnt like playing with me so much now and its pretty lonely over here all by myself even though I do have desired toy...maybe snatching isnt such a good idea and its more fun to be a part of everything with everyone together sharing, etc). Perhaps shortly later, it can be talked about (We really liked that toy and its so hard to wait sometimes isnt it? - What can we do next time we want a toy that someone else is playing with?, etc - If other feelings were involved or passed hurts came up, those too can be addressed).
But I will add one thing that I found very useful to 'say' - because of what the poster above has pointed out (about how sharing is pretty complex and hard for smaller ones to understand) - I read this a readers digest once (it was actually a very good article that also talked about how not to use manipulative praise with our child - very alfie kohn! - Surprised me! hehe)...
We often have friends over at our house. I find with my son I have to especially prepare him for everything - transitions, etc - So when it comes to 'sharing', one thing I have noticed is how most people I know just shout 'SHARE' to their children (and how despite this, they have to continue to shout this!)...This certainly wouldnt be 'helpful' to my son either. Its non-descriptive and once again, the concept is hard to understand in the first place so shouting it to your child really doesn't help. The RD also explained how something is said to a child - and how they actually might hear it. When we say 'share' to our child - what they really hear is 'Give away all your stuff'. So what they said is better to say/explain is 'XXX is still your toy, so and so would like to play with it for a little it, but they will give it back because xxx is still your toy' - something along those lines. And I find that this really does help. My son is happy to know that that is still his toy, and that he will indeed get it back - and so is happy to let so and so play with it for a bit!
For very 'special' toys (my son has a lovely for example) - it might be best to explain to a child that friends are coming over and what they will do when they come over and that perhaps if we don't want so and so to play with special xxx - then maybe we could put it up in a special place whilst they are over so they don't.
I even find now though, that my son is nearly 3 and a half years old - that he does not mind sharing his special stuff becuase he really does understand sharing much more now.