Google is apparently testing placing AdWords ads at the bottom of the search results, again. A WebmasterWorld thread has two people reporting seeing this recently.

One said:

Scott added:

Google has tested this in the past. Back in 2005 and 2008. Here is a screen shot from 2005:

Forum discussion at WebmasterWorld.

Update: Here is a picture from @everfluxx:

Plus there are more pictures from readers in the comments below.