My site has tanked as well on about 98% of my main keyphrases that had been #1 to #4 in the rankings. Now they are 5th to 8th page or worse down in the rankings behind, for the most part, garbage. What's interesting is my homepage went from a PR4 back to a PR6 on Friday. The last time the site was PR6 a few months ago, I had #1 keyword for nearly 100% of my main terms. I thought I'd move up or down a couple of spots with this update, but never imagined it would tank me again. Google traffic is down about 90% so far today. Hopefully will get bumped up some before everythings is said and done. Also of note, I had (and still have) a huge influx of Googlebots on the site this morning, right after the rankings shuffled. I haven't seen this many Googlebots for about three weeks.