-- Relies upon template files (instead of preprocess functions) to implement Bootstrap classes. This means you won't get much Bootstrap styling beyond the basic blocks and other elements themed by the template files.
-- Doesn't utilize the correct structure for including external APIs, meaning that it will (probably) never be a full-fledged project on drupal.org (and thus not benefit from community support).
(This is from http://www.kalamuna.com/news/twitter-bootstrap )