Tumblr just updated again, and the new features are pretty terrible. The text editing controls have been hidden behind a weird popup, they changed the title font to what I'm pretty sure is Buzzfeed's native title font? It certainly looks like it. And they swapped the "cancel" and "post" buttons' positions on the post editor. Among other things, I'm sure. Tumblr has a history of really terrible updates and being bad at building a functional website -- and I have some conspiracy theory ish thoughts on why that is.
I think the non-functionality of Tumblr is actually, at least partly, a secret feature.
One of the things I've often been annoyed about with Tumblr is how difficult it is to search for old posts. The native search feature only returns original posts, so you can't look for a particular response to a thread you're interested in. The notes on any given post only display a couple dozen at a time, so you can't easily use ctrl+f to find a particular response in a post with thousands of likes and reblogs. A google search for a post on a specific Tumblr blog returns links not to a specific post, but generally to a page on the blog -- like www.txwatson.tumblr.com/page/9 -- which almost certainly is no longer the page the post you're looking for is on by the time you do the search, because Tumblr's reblog functionality means the pile of content at the top of any given active blog rapidly buries everything beneath it.
That means Tumblr functions in a way that is basically the opposite of what everyone seems to agree is the major drawback of Facebook -- it's not there forever.
A potential employer, even if they find your Tumblr, is unlikely to find a cross-section of the most embarrassing things you've ever done. If they're really, obsessively committed, they're going to see a cross-section of the last few months of you. That means an embarrassing thing you did or said in 2011 just isn't there to be publicized the way it is on Facebook.
URL changing helps accomplish this, too. And it's pretty easy to re-make your blog if you want to trash the whole timeline. Tumblr gives users the ability to be themselves in an online space in a way that generally tends toward ephemerality -- a user can go out of their way to preserve aspects of their presence that they're particularly proud of, and it's possible for aspects to hit some level of permanency even when the user doesn't want them to, but generally, things go away on Tumblr in a way that they just don't on Facebook.
This logic applies to the shitty messaging system, the shitty tagging system, and probably to their apparent persistent efforts to break every third-party effort to make Tumblr work the way users expect it to.
Now, I'm not sure that all this is okay.
If it's true that this is what Tumblr is doing, maybe they should be more transparent about it. Granted, it's possible they feel like it would lose some of that functionality if it were public -- people might be more zealous about creating records of content if they knew it was meant to disappear on them -- but I feel like we're pretty well acclimating to a cultural understanding that not every aspect of life ought to be fully recorded and documented for future public reference.
I mean, look at Snapchat.