I have learned recently that it is very important to vary your anchor text, or else google might look at them as not being naturally created. I was on a webinar with Amin Motin, ( jons manager) and he was speaking of this very topic.
I have not implemented his steps myself as of yet, but I sure do plan on it for my backlinking approach. I do feel it is important to always mix up the keywords, and phrases you use when droping your link onto places such as blog posts,and forums. I have always done that method even before it was popular. I always thought that if you used the same keyword over, and over, and link it back to your own sites then that would be like spamming ( or over using the same KW), guess I was not too far off maybe
I did also learn that when doing web 2.0 property backlinking, changing the anchor text can also have long term helpful benefits.
Hope my answer helps with this topic question