Can I say, that this type of discussion happened at the back end of June over on the Adsense 'support' (I use the term loosely!) forum.
People's CTR had dropped and they were noticing that their today's earnings would increase and then drop X amount - like clicks had been shaved.
People were mistakenly thinking this was down to the Text Ad change, when in fact it appeared to be a Google 'error'.
My CTR has halved which started on the 19th September. The same thing happened from 30th June, until around the 6th July, but it was worse back then. I've not been effected quite so much this time. Whilst a colleague of mine who has the same themed site, has had no change at all. Text ads have changed the same on both sites.
IMO, any ad changed has not suddenly made less people click the links, but more to do with the same thing happening again that happened in June/July.
The reason? An interesting theory put forward was to do with Google's financial Quarter. In that April/May/June was below what it was last year. So they've shaved clicks off random X accounts to make this money back. Of course, the reply to this theory was that, if that was the case, then Adwords users would get their money back, but that wasn't appearing to be happening.
You can make your own mind up on this, but it's quite apt that it's happened again, coming towards the end of the 3rd Quarter of 2013 - July/August/September.
Take note, that people were putting this all down to ad changes, nessie, enhanced text ads etc, when in my view, it's not down to that at all. It's either a genuine Google problem they haven't yet fathomed out, or something more sinister.
Like a poster above said though, this did rectify itself within 2 weeks. People such as myself had the problem from around 30th June to about the 6th July - some others had their problem from around the 19th June until the beginning of July.