Is it true if you place a lot of adsense ads on the top of your page, or site, that you may be banned from Adsense?
What do you mean by a lot? You can put as many as you want anyplace on your page so long as it's within the total allowed overall by Adsense. https://www.google.com/adsense/support/bin/answer.py?hl=en&answer=9735
Someone hinted here that they placed like 3 adunits on the top of their page, and G banned their adsense acct.
Where? The quote I gave is from the link under it... which is a bit more official then someone hinting around at something. Chances are it was not the three ad units they placed there but something else. Generally when someone gets banned and they post about it here, there is more to the story then they are letting on. Read the OFFICIAL help files, FAQs, and terms of service, and just follow those. Though, keep in mind, putting three ads at the top of your page will cause MANY people to click the BACK button rather then an ad.
if done badly, it can be an horrible user experience and then yes it's a cause for at least the domain being disabled of adsense, but after a few times (or maybe first time) your account can go too with the reason being only that your account poses a risk to adsense advertisers, so you're out, no appeal. It happened to several friends and you can read some here on DP, even though most people prefer to think that it is not true, they feef safer that way.