Belle, we have tried the reward/take away system. The 'take away' aspect did make a difference for a short time, but it wore off quickly. I wouldn't recommend it.
We have also tried the natural consequences system, where you would take away the legos as you mentioned, but that either produced indifference (there are so many other things to do) or a fit as you described. Sometimes I just had a hard time thinking of a natural consequence for certain behaviors. (Some are very clear as in the lego scenario.)
I have a similar thread going, which you can see here:
http://giftedissues.davidsongifted.org/BB/ubbthreads.php/topics/51487/1.html. We are currently trying instant rewards, and have had some success with it so far. Grinity posted an interesting sounding link, but I haven't had time to sit down and read it yet.
I model polite behavior consistently for my children, but they don't always choose to emulate it. My DD5 doesn't usually choose her behavior based on what makes her family happy, but more on what is most important to her at the time. She can be quite generous about pleasing others, but that is not her prime motivation. Maybe it is an age thing, as I remember her being much more a people pleaser at 3 than she is now at 5. Now she is like a little moody teenager, LOL.
