Google ads, search boxes or search results may not be:
1> Displayed in pop-ups or pop-unders
2> Obscured by elements on a page.
Condition one might seem like splitting hairs, but if appears out of nowhere then it's pop up regardless of position on the screen. As for condition two, if turning the layer/div visability on and off does not count as 'obscuring' the advert then I need a new dictionary.
There is also a choice peice about using artificial methods to increase page views eg the Ye Old Meta Refresh trick and this also applies from the look of it. The only saving grace that I can see is that the adverts do not interfere with page navigation, otherwise Google would really be miffed.