Not much to argue with in the original post; it seems self-evident. One's footprint on the web is (obviously) the stuff that one puts on the web, which is a general working description of what a blog is.

The debatable issue is whether one can really form useful impressions based on a blog, or email, or a chatroom, or a cyberfuck, or whatever. about which more here: http://frosch.com/fcb2/index.php?p=4