ZonkerWilliam recommends a bulletin from the American Institute of Physics, which discusses a study noting that recent spacecraft, such as NEAR, appear to display velocity anomalies
much like those seen in Pioneer 10
(which were observed beginning ten years ago). The anomalies amount to up to 13 mm/sec., with a measurement accuracy of 0.1 mm/sec. Quoting: "A new look at the trajectories for various spacecraft as they fly past the Earth finds in each case a tiny amount of surplus velocity. For craft that pursue a path mostly symmetrical with respect to the equator, the effect is minimal. For craft that pursue a more unsymmetrical path, the effect is larger."