Yahoo! acquired blogging community site MyBlogLog (see Danny Sullivan’s discussion of the site and how it works). Here’s a Yahoo! Developer Network blog post on the acquisition.
I’ve argued in the past that Yahoo!’s existing blogging tool (360) is the weak link in Yahoo!’s otherwise very strong social media strategy and that it should buy Six Apart or WordPress.
Google owns Blogger, which was recently upgraded and taken out of beta.
Screenwerk 
June 20, 2007 at 7:50 am
[…] I forgot to discuss MyYahoo!, which could be an important property for the company as well as the need to bring a “center” to its social media strategy, either by buying a network or building one with better tools (e.g., blogging software). […]
October 25, 2007 at 5:40 pm
[…] social networking/blogging platform 360 is finally going away in favor of “Mash.” I argued previously that Yahoo! should have bought WordPress or Six Apart. Mash shouldn’t be positioned as a […]