Thus spake Andy Isaacson (adi@hexapodia.org):
noisetor-01 was pushing 300-400 Mbps of traffic from 2012-02-15 through 2012-04-13. Since mid-April we've seen traffic decrease significantly; over the last week, our daily peak has been 260 Mbps (versus 450 Mbps in March) and our daily trough has been 100 Mbps (versus 300 Mbps in March).
The traffic levels dropped off in a smooth fashion over a 10 day period, April 15-25 if I read the graphs correctly.
Has there been a change in the routing algorithm, or any other network changes that might explain this drop?
The loss of non-TBB Torbutton users might explain a drop post Apr 20th, when their ability to move tabs around was borked by FF12: https://bugzilla.mozilla.org/show_bug.cgi?id=715885#c33
But otherwise, according to https://metrics.torproject.org/consensus-health.html, all 5 bw auths are voting, and I have not changed the algorithms.