A natural link (ie you write something and some other site links to you), which should be the most valuable link in Google's eyes, will almost always have the anchor text to the link as either the name of your site or something generic like "click here" or "this site" or "follow this link" or "source". If a site writes something like "John's site has a great post about widgets", 99% of the time the linked words will either be "john's site" or "great post". If you are doing the linkbuilding yourself, you would use "widgets". Of course having keywords as your anchor will help you rank for those keywords but it seems like linkbuilding rather than natural incoming links. I don't think Google can tell the difference though. Thoughts?
Using specific keyword to avoid penalties for overused Anchor Text, you need to vary you anchor text to avoid having the links appear unnatural
If "Anchor text" in your comment is following the link or your link is relevant to that particular keyword then it's fine .If not it will look unnatural as linking just for the sake of getting backlink.