designaweb - 8:55 am on May 3, 2010 (gmt 0) [edited by: tedster at 10:48 am (utc) on May 3, 2010]
Here's another observation, allthough I am not sure whether it's related. I can't really see the connection, but perhaps other find this usefull.
I've got a niche location related site, 3 levels deep and available in 16 languages. On 21st of April, traffic was down roughly 80% on some of these languages. On the 27th traffic was back up, but still 30% less then before. Not all language sites were affected:
EN-UK (possibly affected)
First ones I spotted were the DE-* variants. I am using rewritten content for the AT/CH versions, focusing on different phrases (synonyms), so I thought Google thought of these 3 pages as duplicate content and penalized them. However, the Portuguese, Polish, Swedish and Finnish sites are also affected, and although the content all derives (translated) from it's EN-US source, they are all unique, and still affected. I am using 2 seperate servers (on completely different IP's, but no pattern can be found in this either.
Still clueless, will post back here if I find some more hints on what's going on in my case, but for now I hope this helps anyone.
[edited by: tedster at 10:48 am (utc) on May 3, 2010]