It is interesting and highly significant that almost everyone who blogs about SL or posts photos from SL on Flickr, does so in their avatar's name. [More later, it's 3:30am and I am happy but exhausted after seeing Grace McDunnough perform at SL Pride.]
This is of course simplistic and reductivist, and intentionally so. These posts are not meant to be fair and balanced essays to be delivered de haut en bas, I am gathering talking points for a workshop. However, the observation stands — with one qualification: it depends on the speaker's relationship to their audience.
When [Botgirl|Grace|Dusan|whomever] blogs about SL-ness and identity, they are by and large speaking as one of us, peer to peer, within a community and a shared culture. They can assume that we will to a large extent share their experience (by being inworld) and interests (by being curious enough to be reading their blog) — though this does not mean that we necessarily share their values (cough Prokofy Neva cough).
When they talk to "outsiders," they often do so in their RL names, for example Hamlet Au's New World Notes lists both of his identities. [more later]