Volker,
I have found just keeping the most recent reading insufficient in the sense that you end up with too many outlier readings.
What I do is when I have 10 readings built up, I spit out a reading which is the average of those 10 readings. Then I dump the oldest 5, and wait until I get 5 more before I emit another reading. You end up with readings about every 2 minutes or so, with a lot less crazy variance.
Just something else to think about. the outliers can play havoc with rules you may create in the future for notifications/alarms, etc.