How long do you think you have to keep the same anchor text in order to get good results? for example... if I'm #1 for "cars" and mainly from IBL's from network, if I change that anchor text to "automobile" after a certain amount of time how much will this effect my rankings in the SERP's?
depends on what your rankings were before the network. That being said, I added in 2 ads 2 days ago to the 5 that I had already, and I saw a decent sized drop today (less than 2 days later) (EDIT: and when I say drop, I mean a bad drop for the 5 that I had before, not a good increase for the 2 phrases that I just added)
Check out this thread about my recent experiences using the coop & serp results with anchor text rotation: http://forums.digitalpoint.com/showthread.php?t=5382