If you are using adsense tracker like asrep or other, you will can see ip address from visitor who click the ads If you get two clicks from same ip address, need to reporting it to google or not? https://www.google.com/support/adsense/bin/request.py?contact=invalid_clicks_contact is it the more often we email google the better??
No. I think two click from same IP is not a big problem. If it is university or company static IP, you do not even think about it.
I think you don't need to contact google. If you see a click bombing like activity, then you contact google. If someone finds the ads on your page interesting, then he or she might click on more than 1 ad. No need to worry.
2 clicks not a problem... no need to report to google... but don't think of using proxy and clicking twice because google will definitely find out..
In some areas whole small towns or villages have one IP. Can you imagine local blog or forum? All clicks are from the same IP...
I wouldn't worry about it. On rare days, I'll have over 100% click-through on a site and google's never had a problem with it (or made the clicks invalid) because all the traffic is honest traffic.
No need to report to Google. Imagine the amount of reports they would get if everyone has to email them for something like this