I've got a nice tight Twitter user name, @nelson. Unfortunately I'm not the only Nelson on Twitter and my mentions timeline is full of people trying to talk to Nelson Bocaranda, Nelson Rubens, Nelson Koenji, not to mention everyone in South Africa talking about being "@Nelson Mandela square". It's irritating.
One partial solution that either Twitter could implement or could be done in a Twitter client; filter on reply-to metadata. The mentions timeline includes everything with the string "@nelson" in the Tweet. But many mentions also have a "in_reply_to_screen_name" or "in_reply_to_status_id" set in the metadata. I'd like to not see Tweets which are clearly in reply to someone else.