Struggling online giant Yahoo! this morning revealed its plans to purchase Tumblr, a blogging service with more than 300 million unique users. In a quirky press release, the firm said it wouldn’t “screw it up,” and would instead allow Tumblr to be independently operated as a separate business.

“Tumblr is redefining creative expression online,” Yahoo! CEO Marissa Mayer said. “On many levels, Tumblr and Yahoo! couldn't be more different, but, at the same time, they couldn't be more complementary. Yahoo! is the Internet's original media network. Tumblr is the Internet's fastest-growing media frenzy. Both companies are homes for brands—established and emerging. And, fundamentally, Tumblr and Yahoo! are both all about users, design, and finding surprise and inspiration amidst the everyday.”

Yahoo!’s promise not to “screw it up” could be a reference to the firm’s 2005 purchase of Flickr, arguably the best photo-sharing service online, but one that has been basically ignored by Yahoo! for years and is starting to be overshadowed by rivals like Facebook. Clearly, Yahoo! is doing things differently with Tumblr, and the decision to allow the company to continue independently closely mirrors Microsoft’s acquisition of Skype.

“Tumblr founder David Karp will remain CEO,” Yahoo! said. “The product, service, and brand will continue to be defined and developed separately with the same Tumblr irreverence, wit, and commitment to empower creators.”

Tumblr gives Yahoo! a big entry into two key parts of the online experience that have been thus far lacking for the firm: social network-style interactivity, with user-created content, and popular mobile apps. Yahoo! says that it will bring Tumblr’s 108 million blogs and 50 billion posts to its media and search experiences, and that Yahoo! personalization and search technology will in turn help people better find relevant content on Tumblr.

I can’t vouch for the value of Tumblr, but the acquisition makes sense. That said, Yahoo! should spend at least that much cash improving the quality and reach of Flickr, as well: That’s a valuable in-house brand that has languished for far too long.