The repeated manual clicking thing is to prevent click fraud. There is no reason why you or your staff/friends should click your own ads (other than occasional troubleshooting) unless you are trying to artificially inflate the click rate.
So I guess the answer is don't think in terms of 'how much can I get away with' but rather 'I don't need to do that so it's immaterial.'
happygeek
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To answer the second question ... it has to do with your industry, the keywords on each specific page of the site (and how much people are willing to bid on those keywords), and the click-thru rate of each of your ad spots. Remember, it's a violation of Google's terms of service to tell others your eCPM, so technically you and your friend shouldn't be comparing. ;) Technicalities!
cscgal
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