Twitter Bootstrap made version 3.x which has some migration changes involved, so it's not a trivial update. However, it's mostly done through renamed classes, so it shouldn't be too hard to accomplish.
In relation to this, Bootstrap v3.x adds a bunch of neat responsive layout stuff that makes it far easier to support phones/tablets/etc. The grid layout stuff would be preferable over the current abuse of tables in the site.vm template file. However, that would definitely be a separate issue!