request for a kill file feature similar to newsreaders

There are usually a few tweets by given users that I want to ignore without unfollowing the user, it would be very useful to be able to ignore tweets based on substring patterns or regexp, either for a given user or for all users.
The same could be useful for highlighting certain tweets.
This could be either implemented on the service itself (webpage and api) or it could be implemented in the 3rd party applications, e.g. Tweetdeck