the click bomb thing is the only thing i'd worry about. it sucks that adwords only allows 20 or so IPs to be blocked. never checked if MSN allows IP blocking. all someone needs to do is set multiple clickbots on various shady/foreign shell accounts running through a range of IPs (50 or so) to sleep and 'click' at random intervals. that will fuck your shit up. they could run random searches w/ various terms and scrape for your display URL so they aren't always hitting the same keyword.