It was a Panda update....Matt Cutts from Google confirmed it on his Twitter....
http://twitter.com/#!/mattcutts/stat...05069748559872
Cutts also issued a weather report earlier around October 5 there will be flux in the serps over the next few weeks.
Websites will go up and down over this period....losses may turn into gains into losses into gains.
Its part of the Panda whitewash to eliminate small webmasters from the internet. The only real winners here are google properties or members of the OPA.
For those talking about building backlinks...it is irrelevant...Panda does not count backlinks...its a artificial neural learning algorithm. Its also run manually from time to time and only runs against a small percentage of the web at a time. If you were not affected it may only mean you missed the scan.
Right now google do not give a stuff about adult...Panda is about mainstream....any adult caught in the middle are only a byproduct.
The Adult version of Panda is due next year...thats when you can kiss away your business.