The exit of Twitter CTO Blaine Cook after a big weekend service outage generated a lot of discussion at the Web 2.0 conference in San Francisco this week.  We caught up with David Mandell, co-founder of the social-browsing startup Medium, to get his thoughts on scaling the infrastructure for a company whose traffic is growing explosively. At the end of our discussion, Mandell tells us that the company is getting ready to roll out its own new architecture next week.