How many different anchor text themes should you have? Here is an example that will make my question more clear: I have a site about widgets. So I can develop anchor text that says: buy widgets. But I also have other pages within my site that are more specific and I would like to have anchor text thas says: buy product xyz. So, using this approach, I could have hundreds of different anchor text for links (depending on how many products I have). Is this good? Bad?
Personally I try to vary it as much as possible, with link exchanges try to make them different every time while keeping the same/similar main keywords. If all anchor text is the same I'm certain there is a penalty for this. I've had clients sites that have had 6000+ links with a fairly uncompetative term in the anchor text. They couldn't get ranked at all.
I try to do 10 of a certain phrase and then switch it. This strengthens a certain keyphrase w/o penalties.