I initially thought that this service can filter posts by keywords and remove duplicate contents (like we always wanted from GReader), but obviously they just let you filter out the unpopular posts that are ranked by their "PostRank" (proclaiming, "Google, buy us!").

Anyways, it's a great service to try out. :)

Screencast: http://www.aiderss.com/blog/screencasts/rss-import/

I tried it and the PostRank is just a combination of no of comments, backlinks, diggs, delicious bookmarks. It's also extremely inaccurate and doesn't work for some feeds. I imported my Google Reader OPML and only 50% of the feeds were already indexed; the most important posts were old and had 1-2 backlinks.

Even if it worked very well, you'd only get a feed of the most popular posts from a blog.

Given that Yahoo has been adding all kinds of components like Regex modules to Pipes, I'd be willing to bet that it'd be able to do some complex filtering now. I've never played with it to do anything more than filter RSS feeds by category or keyword, but I imagine you could get it to remove dupes too.

http://pipes.yahoo.com

Also it was slashdotted here:
http://slashdot.org/articles/07/07/24/2241222.shtml