On Saturday March 9th, 2013 there was a dip in login according to the Metrics Dashboard
Sign Ins were down 40%
3/8 37,978
3/9 12,919
3/10 31,675
PHX1 and SCL2 Statsd graphs look good across various components
We can see a slight reduction in activity, especially looking at the Session Context wsapi graphs, but this doesn't look like a 40% dip.
No Issues repored in bugs, Twitter, or IRC http://irclog.gr/#browse/irc.mozilla.org/identity/218536
Filed Bug#849944 to get help identifying the source of the dip.