I find it to be hilarious just how many people try to leave “glowing” (though often totally non-sequitur) comments on my blogs (always the older ones, not something recent) that are nothing but transparent attempts to get a backlink to their website. Sometimes I’ll approve the comment after editing out the backlinks – it would be fun to see if they ever check up on it.
I don’t support backlink swaps just for the sake of a backlink. If you actually like something I wrote enough that you re-blog it with the link back to me – thank you. I’ll do the same when I see blogs by others that I feel merit a shout (and I do this quite often). But, all comments are screened on my blog for just this reason – I will not let you use my blog for nothing else than improving your Google Search position. That is not the benefit my blog exists to pass on to you.