don't load the class until you need it

This is at the top of the module code, bare, and hence loaded every single page request:

require_once (dirname(__FILE__) . '/twitter_pull.class.inc');

Yet the only place I can tell that you need the single class that's in that file is within twitter_pull_retrieve(). Why not include the code then -- and it should probably use a module_load_include() too.