Back in June of last year, Google began testing bucketing related ads on the site bar. They expanded that test by displaying searches related to later on in the year above the Google Map on the right.
Now there are additional reports of Google testing even more grouping of the AdWords ads on the right by segments or categories.
Scott from the WebmasterWorld forums posted a screen shot of what he described as Google attempting to achieve "higher relevance from a very general, ambiguous search."
Mick from Search Engine People also noticed this from Google and posted a screen shot.
Forum discussion at WebmasterWorld.