MrFlex2600 - 4:50 am on May 17, 2011 (gmt 0)
My daily traffic has dropped from 5000 visitors a day to 200 visitors a day.
Sounds like a Google penalty of some kind. I had exactly same problem with one of my sites in February 2007.
The sites was growing very fast and it went from 0 to over 3000 unique visitors/day in 10 months, and then suddenly my traffic dropped to about 300 uniques/day OVERNIGHT!
EXACTLY 4 months later Google lifted the penalty and my traffic went up from 300 to 2000 uniques overnight.
Since then the site never went back to 3000 uniques/day. Last month the site was pandalized and now I'm at about 1200 uniquies/day.
That's why NEVER put your energy into one site. NEVER!
Instead of building one large site, just create 5 smaller sites. If one of them get penalized/pandalized/googlized/whateverlized... you'll have 4 more.