i think it looks best at the side or navi bar. and its best to specify that it's an ad so that people who click it and find something... um... disgusting, you won't need to take the blame.
personally, i think it deserves a 6. sure it helps with finding stuff for homework and other things you need to research about. despite my rating, i think it's the best search engine ever. but why a 6? because it has failed me countless times and one time i suddenly downloaded a virus! so google, thank you, but no thank you.