There’s a very nice chart over at the Heavens-Above satellite tracking site site showing how the recent boosts have increased the Station’s permanent orbit – by almost 50km! ATV Johannes Kepler has been the ‘engine’ behind the majority of this increase.
Station Average Altitude Increase Credit: http://www.heavens-above.com This plot shows the orbital height of the ISS over the last year. Clearly visible are the re-boosts which suddenly increase the height, and the gradual decay in between. The height is averaged over one orbit, and the gradual decrease is caused by atmospheric drag. As can be seen from the plot, the rate of descent is not constant and this variation is caused by changes in the density of the tenuous outer atmosphere due mainly to solar activity.
Full details via Heavens-Above.com