Some people think that MS will have security issues around RSS:

This is actually pretty sad. MS has not even released the damned RSS portion of Long Horn yet and people are already saying there are going to be flaws! This kills me as there is really no reason why there should be any security exploits unless the devs screw up somewhere along the line. Are we really getting to be this knee-jerk about MS security?

The author above is correct; I can't see how MS could open up anything that's not already open. The main risk I can think of is existing browser based problems with scripts (which BottomFeeder is immune to :) ), or some currently unknown issue with a media player (MS or otherwise) combined with a hostile enclosure. What am I missing?