Prevent post-dated posts from staying at the top of aggregated feeds
Here's an example of what's happening: http://skitch.com/cweagans/gh54y/sparrow
That post will stay at the top of planet until after January 31, 2012 at 5:35pm. Letting people do that seems like the wrong behavior, but I don't know how we should fix it.
Edited by drupalbot