farmboy - 5:58 pm on Jan 27, 2010 (gmt 0)

There must have been a lot of advertisers shut down in order to make CTR fall by 50%.

CTR isn't a factor in this scenario IMO. If someone's CTR has decreased, that's another discussion.

But on the subject of the number of advertisers shut down, the article I read indicated it was about 30,000.

And just for some trivia, the same article indicated 30,000 was about 5% of the total number of advertisers. If my math is right, that means Google had about 600,000 advertisers and is now down to about 570,000. (I don't if that is active advertisers or includes accounts that are just sitting idle)

FarmBoy