For what it's worth, Maemo Mapper does try to "ignore" GPS data that is "sufficiently close" to previous data, based somewhat on the "dilution of precision" (roughly correlated with the estimated error) of the GPS fix. But the effectiveness of that varies quite wildly from GPS receiver to GPS receiver, depending on how well a particular one measures DOP. And the code tends to err on the side of safety, so in many cases, it will plot data that a human would probably throw out.