Planet13 - 9:17 pm on Nov 21, 2010 (gmt 0)
Also, I can't see how previews would make the bounce rate go lower, only higher.
Precisely. The bounce rate for Search Engine Traffic DROPPED from around 65% to around 12% on October 19th.
Direct Traffic remained about the same.
Referral traffic dropped slightly, but I expect that is an anomaly in analytics as well.
Have you seen something in the past where all of a sudden, GA would just start returning garbage numbers for one of the main metrics for no apparent reason? (aside from the above-referenced case where GA stopped supporting the urchin code and moved the the ga.js script).