graeme_p - 5:16 am on Jan 24, 2012 (gmt 0)
It seems to me you're fine with two ads above the fold. If it's a 728x90 in your header and a 300x250 in your right column next to your content, you're good.
I have been hit, and I only had a single ad above the fold. A 336x280 above the fold and to the left seems to be fatal. It is fine on desktop resolutions (most of my visitors) so Google are presumably catering to smaller screens than I have been.
@Marketing Guy, I think it is this: lots of terms (glossary type site) and both main gainers keep ads subtle (on the right, and mostly text link ads above the fold in one case, and no ads in the other case). NO other changes in my niche except smaller (my size) competitors seem to have been hit even worse either on this change or at some point before it.
Given the date, lack of any other apparent changes, and also minor gainers - my best single term I was in second to third place on Google UK, now behind the two mentioned, a .gov.uk and a site that only has a single banner above the fold (another banner and text links means they have plenty of ads, but not above the fold).