Tumblr has several ways for one user to send text to another user with varying levels of how public they are and who can respond. It's all over the place and many users are jaded by how dysfunctional it is. These have changed several times over the years and there have been a few major browser extentions/user scripts designed to overhaul these (xkit, missing E).<p>@mentions/tagging: A user could add another person's username in the tags of a post, and quite a few people "track" the tag of their username and could see and reblog the post from there. @mentions are newer but work similarly, without the user being mentioned needed to do anything on their end.<p>Reblogging: Append a message/reply at the end of the post. The first user can then reblog the second user's post and add to it, resulting in a loose thread. I say loose since a third or higher number user can reblog and the conversation chain can become wildly different once a post hits a high number of notes. Reblogs are always public.<p>Replying: A user could "reply" to another user's text post which would be visible in the notes of the post. The OP would get a notification, but there's no way to reply directly to that reply. Most users used these as a quick one-way (from follower to OP) type of communication. Tumblr confusingly removed replies altogether a couple of weeks ago stating they were "rarely used".<p>Fan-mail: Completely one way communication from one user to another directly. Fan-mail is private and doesn't post on your blog. Users can send fan mail back and forth, but there's no concept of a conversation chain. Mostly used by spam blogs ("test my game", "do this survey").<p>Asks: A user can send a message to another user, as themselves or anonymously if the other user has it enabled. Asks can be answered privately, or publicly, which makes a post on the answerer's blog that others can see/reblog.
Seems pretty pointless since there are Asks/Fan mails already. What does instant messaging have to do with a blog service anyway? Tumblr's strength is being a content publishing platform, an easier Wordpress/Blogger. So they should be developing new types of content to publish. For example polls would be cool (since Twitter added them recently). But IM functionality is just a distraction from posting new content.
For those in the know: how is Tumblr been performing under Yahoo? I've read that the CEO of Tumblr was distanced from Meyer, by placing him under another Exec, but I know little of what their grand plans are.