I've noticed that my adsense earnings at times increase as a result of just "impressions" and no clicks (even if it is only a few cents). Is this normal? And does Google pay it because there aren't clicks (adword users) to generate the income?
it is pay per click and not pay per impression. it happened to me one or twice only, doesn't happen often.
adsense pays via clicks or per 1000 impressions. some of you noobs need to read the official adsense help site.
Well it's also advertisers who have ordered a site targeted ad campain and have chosen your site to be part of their campain. The advertisers pay a CPM. But i think it's going to change soon. Source: http://www.google.com/ads/sitetargeted.html