Or would it be better for the representation of ones social network be incomplete on any particular site. (E.g. some people are only on facebook friends, or twitter followers, or G+ circle members.) So post deduplication is handled by only subscribing once on ones preferred service..
Or alternatively the poster could just pick one site and post there and make everyone check multiple sites to keep up with everyone they want to pay attention to.
How annoying is social network post duplication