Two things Google reader does wrong (in my opinion):

If two of your friends have shared the same post, it appears twice in your shared items.
If you follow a blog that one of your friends has shared a post from, you see both the blog post and the shared post.

I can see why there might be reasons for this, but on the face of it, this is just plain stupid, and even if it’s not plain stupid (e.g. if the comments are different on each post), there has to be a smarter way to handle this. I don’t want to read the same post twice. I have a hard enough time being patient enough to keep up with my feeds as it is.