Interesting, I recently worked on Project4Awesome, a community event on Youtube. Our site used a single MongoDB node on a relatively standard server and handled >100k pageviews in 24 hours with no caching. That being said, I've worked with Mongo before and know many of it's issues, so I knew what to expect.
Though, without meaning to criticize the author too much, increasing various ulimits should be standard on pretty much any database server, I would have thought?