How many ad units can be used on one page? Does number of ad units effect earning? Does it have to do anything with CTR?
You are allowed to place up to three AdSense for content units on one webpage. You may also place a maximum of three link units and two search boxes on each webpage. https://www.google.com/adsense/support/bin/answer.py?answer=9735&topic=8425
based on my own testing, number of ads do affect my CPC, but not too sure about the rest of google adsense user. and for the CTR, the answer is Nope. It does not affect CTR directly.
