I think it's a good idea - just need to have a set trigger as to what is defined as a hot/popular topic. Certanly 10+ replies constitutes as a popular topic, however we've all seen the topics being raised from 2007
So setting that number alone can't be the trigger.
Check out the following thread: http://www.vbseo.com/f10/new-vbullet...ter-api-28015/
I'd just be concerned as to the amount of spam that could send out if posts are not monitored before being tweeted ya know?