Google would not randomly bann someone with incom streams over $700 or $3000 because to get that much, that means google probably made over 2,000 with the $700 and possibly up to $8,000 on the $3,000...all depending on how much of the pie they got. they would not ban them if they didnt deserve it. NOTE: my numbers of $2,000 and $8,000 are probably not 100% accurate, but given the fact google is making a % of each click, its most likely more than half.
that type of repetitive clicking is automatically discounted by google... you can't get banned for it.
I think if you earn a lot of money from google, them will pay attention to your account, so it is normal, but carefal not to break the rule
"Invalid Clicks" is just a broad term that Google uses to ban your account. Did you friend participate in some traffic exchange programs? How about HYIP for impressions? Did he participate in that? If his sole intention was to just make money with Adsense WITHOUT providing good content, even I would ban you / your friend. Ask yourself, if you were Google and someone was screwing around with your advertisers, what would you do?