glitterball - 11:45 am on Jul 29, 2010 (gmt 0)
After yesterday's irrelevant Ads and low CTR, everything seems back to normal (similar to the rest of this month) and I'm seeing good Ads everywhere again.
Is it possible that a feedback loop could be causing these periods of poor targeting? Okay, I only had one day this month, but I had to suffer a few months of poor Ads earlier in the year.
e.g. If CTR drops below a certain level, then Google decides that the Ads must be badly targetted and starts showing different ones. If this causes a brief spike in CTR (as could be the case on a site that attracts a lot of regular visitors), then Google shows even more of the "new" Ads, which would eventually lead to an even worse CTR.