Dave, if you read this – Twitter is not email. This is the beauty of it. The need to sum up something in 140 characters or less is a strength, not a weakness.
If you want to start attaching sound or pictures to it you break the beauty of it, the immediacy and the poetry.
Turning twitter into a multimedia extravaganza would break it. If you want to do that sort of thing then mobile post to your blog, then people with RSS readers on their phone can follow you.
It’s like trying to improve a screwdriver by sticking a laser beam and a jet engine on it.
I’m not convinced that it even needs tagging.