The ads (and number of ads) that you see at the top can easily vary from one search to the next, depending on the competitive landscape at the moment of the search.
They've been varying for quite awhile. From AWA in this Google Page Formats thread:The ads (and number of ads) that you see at the top can easily vary from one search to the next, depending on the competitive landscape at the moment of the search.
jimbeetle, I actually meant the above quote in terms of the normal max of two ads up 'North'.
Anything other than zero, one, or two ads up there would be a case of sharp eyes having spotted a test in progress. ;)
Testing prior to launch?
That would be news to me...
AWA
6months-1 year ago (memeory isn't that good), saw the same thing.
The 3-4 ad formats have not been implemented yet.
My guess is that it's Google gathering data in certain verticals (they're almost always very commercial searches) for internal layout analysis.
Google testing prior to launch would be news to everybody.
:)