February 2010 collapse

I would really like to know if anybody else has experienced collapse in CTR+ECPM+CPC-wise starting in February (Jan 31 was totally normal day).
Facts:
– Same traffic
– Same advertizers with the same budgets (small niche, everybody knows everybody)
– Everything was rock solid the last year
– Last minutes of January looks normal
… then… February starts and CTR drops 20%, eCPM 25% in one second and has stayed at the new level every since.
Is this something only I am experiencing, or…?
I just cannot figure this one out… If it is penalty (and the level of the jump would support this), why has my CTR jumped down?
Only explanation I can think is that: I have hit some penalty word, which has ""disabled"" some of the ads. But without knowing the exact problem, it’s kind of difficult to "undo".

See original post by 3oltan