1script - 7:56 pm on Apr 1, 2010 (gmt 0)

Let me give it a try:

1. Are your traffic Decline is from USA and UK?
both

2. Is Traffic Drops only from Google or from other search engines too?
Google only

3. Did you notice any decline in GoogleBot Deep Crawling?
not really. But I have to make a note that due to the forum nature of the affected sites the same URL could be 1 level deep when fresh and 10 levels deep when very old. Googlebot appears to come for both old posts and new.

4. Is the traffic Drop is sudden or gradual decline?
Sudden 90% decline on March 15th

5. Is your rankings on your major keywords drops?
Some did but some (~30%) did not. and rank where they've been (or better, actually). It's the truly long tail (1-2 searches per day type) that have completely disappeared.

6. Are your website internal pages caching normally?
I can see new posts cached in a couple of hours. That was the norm for the last couple years.

7. Decline in Indexing Status Of Your website?
Depends on how you measure: WMT sitemap indexed pages seem to be stagnant (40% average) but not dropping (note so self - write that number down over a week or so). site:example.com search though has been completely wacky.

@Gorgwatcher: hope we can get some good data from multiple sites here. Watching only one's own sites can render one insane.