It does not work also for me, don't know why but it display always "Could not connect to Twitter".
I changed the return of _getFeedUrl to
return sprintf( 'http://api.twitter.com/1/statuses/user_timeline.json?include_entities=true&include_rts=true&screen_name=%1$s&count=%2$s', $widgetOptions['username'], $count );
but I am not an expert. I don't know if it is correct, but with this fix now it works for me.
Worked for me too! Thanks Drake.
For everyone else,
in wp-twitter-widget.php
Replace lines 636 to 662 with
return sprintf( 'http://api.twitter.com/1/statuses/user_timeline.json?include_entities=true&include_rts=true&screen_name=%1$s&count=%2$s', $widgetOptions['username'], $count );
Thanks again Drake.