There are so many more issues with Reddit, I'm surprised they haven't been digg'd or myspace'd yet.
One big 'bootstrapping' problem is that the first to adopt a new platform are the people who are _too toxic_ for the original.
While everyone on Digg or MySpace could easily move to reddit or facebook, it is much harder for a subreddit centered around say gardening, astrophotography, headphones or a tv show to just jump to a new website. I do hope that these communities won't be lost when reddit does end up losing its charm and popularity.
Taking down an incumbent is hard, though. Might need deep pockets for a while.