Seems like a cool thing, surely. Well almost. If your social network across different social media services looks like below, then posting the same update on different services makes sense. After all, there’re only a few connections that are common across different services you use and pushing the same update on all services helps you get the message to a wider connection base.
However, if your social network looks like the one below, you are bombarding your connections with the same update on all networks. This can be very irritating for your connections.
My rule of thumb – limit convergences of updates on different social media services irrespective of the overlaps of your connections.