darkmage - 6:19 am on Feb 28, 2007 (gmt 0)

For me, the second last google day of the month is always the worst (some times it starts a few days earlier). It makes sense it terms of monthly budgets, put in the fact Google is located near the last time zone of the world and that's why I think it happens. The end of month tailing tends to happen earlier in 31 day months.
Traffic and CTR are all normal, it's simply a wipeout for CPC. The higher the CPM of a channel, the more pronounced the effect. Low CPM channels barely move.