Nice post :)

I have a PR-2 blog which I rarely update. Still, time by time existing and new visitors come and leave comments on the latest posts. As those are old posts, despite their eagerness to leave comments (as I set my blog to do-follow), the visitors likely could say nothing other than "nice post" or "great job". Do you think I should delete those spam comments, considering that some of them came from my friends.

Most often than not, those ARE spam comments, especially if an URL is attached to their username. If not, then I'd usually leave those comments in.

Yes the URL is there. I notice that even several comments with different URLs attached in a row came from the same IP. They are spams, ugh!

Consider them spam.

I get the same stuff. What I do is leave may be one or two few good comments given by these spammers and delete the rest.