I meant, the title says from a hobby to a startup but I believe it's always been both (it didn't just become a startup, it always has been in a sense). Sorry, maybe my wording was off.
I kinda had a hunch he would be doing this. As it stands right now, Instapaper has a greater chance of making more money than Tumblr, simply because they are selling iOS apps already and the datamining potential is greater (with Tumblr, how do you analyze different blog posts and so on?), such as finding out which blogs are most popular.
Though I am extremely excited to see what Marco has to offer the world now that he can devote more than 10 hours a week.