What is really interesting about Skimmer, is that has been developed by a marketing firm. So I am sure it is a matter of time before you start seeing advertisements showing up on the Skimmer interface.
After making this post I came across another aggregator for the Mac environment. “Eventbox” comes from the folks at Comic Machine. It provides access to Facebook, Flickr, Twitter, News Feeds, and Google Reader. What’s nice about this aggregator that its interface has the feel of an email in box plus the features of a life stream.