I love Tumblr, somewhat for its social features, but mostly for its ease of publishing. A good blogging tool gets out of your way, and makes it so easy for you to publish your ideas and discoveries on the web that you don't even have to think about it. Tumblr does this well. I was one of the first people to write a rave review of Tumblr on Lifehacker in March of 2007, a month after it went live. One of Tumblr's co-founders said that my piece "effectively launched the site." I take pride in that, not only because Tumblr's a great tool, but because its team is located in my hometown of New York City. I've been tumblelogging at scribbling.net for four years now.
Lately Tumblr's been getting lots of attention from name bloggers like Steve Rubel (who closed all his existing blogs and moved exclusively to Tumblr), Rick Sanchez, Dan Patterson, and my friend here in San Diego Mitch Wagner. So when I began an effort to simplify my blog life, I considered switching this blog to Tumblr and making it my primary platform like Steve and Mitch did.
In the end I decided not to, for an important practical reason: the data you enter on Tumblr is locked in. While there are some hacky third-party tools that purport to do it, Tumblr itself does not offer an official export feature which lets its users move their data to another platform should they choose to do so. (Update: In late 2009, Tumblr mentioned a beta tool which can export your data in a limited way, on one platform. Doesn't count.) That, along with some doubts about site reliability and losing my existing posts and their permalinks, made me decide the posts I really care about are just too important for Tumblr.
The practical problem of data lock-in this many years into the game is indicative of a larger philosophical issue. Tumblr treats content more like a social network does than a writing/publishing/archiving tool should—with an emphasis on easy sharing, liking, and reblogging, but not enough care paid to hosting that content in a place where ideas and conversations can live and grow over time, a place where search engines of the future can find it. This is exactly what Anil was getting at in his post, If You Didn't Blog It, It Didn't Happen. Social networks are good for sharing links to ideas, not parking ideas.
Therefore, I will continue to use Tumblr more as a social network than a blogging tool: a place to share links, photos, and videos that I'd like to broadcast, but don't care enough about to give a home on a place I own, control, and intend take with me in the future.
Update: Mitch's response, Why Tumblr, gets to the heart of our different attitudes about publishing web content. Is it "tears in rain" or "books on a shelf"? Both are valid approaches, and the tools you use should suit the one you choose.