I've heard / confirmed at least 3 or 4 different versions of the acronym in the past, but
aprs.org does indeed seem to say "Automatic Packet Reporting System" this week.
http://www.aprs.org/doc/APRS101.PDF still calls it "AUTOMATIC POSITION REPORTING SYSTEM".
Still, a few more variants of (Amateur|Automatic) (Packet|Position) (Radio|Reporting) System to try over the next few years, eh? ;-)
Where do these name changes and protocol updates get discussed / announced? I feel I need to be on another mailing-list
-- Nick VA3NNW