I have only read the first post so appologies if someone has mentioned this before me.
According to the Association of Separated Families, what damages the children is not the separation itself but the rowing before the split. If you and your DH have spared them of those bad moments, it is unlikely for them to get damaged. Obviously, there would be some changes, and big ones, but as long as you reasure them that your decission doesn't affect the love that you have for them or the realtionship with the other parent, things should be fine.
There is a book I found very useful when in the process of finding our feet with regards to DS around the time of the separation. It is called Putting Children First, I can not recommend it strongly enough.
I think DS has benefitted from our separation, he gets more attention than before from the two of us (now the time we have him around is sacred), visiting his dad every other weekend is an adventure he certainly looks forward to, we also have great times together and I think our relationship has become stronger.
ExH and I have kept in very good terms (possible as there were no nasty issues between us, we just fell out of love). We decided to protect our friends as we did with DS: not going into any detail that may make them feel forced to take sides. By showing everyone that we are fine on each other's company, we can go to friends get togethers and even have "family" days out from time to time. This lack of animosity has kept DS' world in its place.