Topic: Multi user site where users can create blogs?

What would be the best strategy to create an app where users can add mini-sites with a blog-like features: feed, picture uploads etc.)? Something fluke Tumblr-lite (no individual styling needed)?
Any specific plugin anybody can recommend? Or a general strategy (I am thinking smth like Nesta or ComfortableMexicanSofa as rack-mounted app.. but would it be good for large number of users)?
Thanks in advance!