@Lappy9000: I've been debating whether or not casters will need a concentration check against coughing all of the time. I'd leave that up to the GM, but I myself would go with: Yes. The coughing will become more pronounced the more the player exerts him/herself. So, if a Magic-user is casting a spell in relative peace, I wouldn't require him/her to make the check (unless it could further the story by making things a little more interesting). But if it is in the middle of a pitched battle or the spellcaster just finished running away from something, I might ask them to make the check.

Note: In most of the games I run, a flubbed spell can do something different or it might do nothing at all.

I'm also thinking of creating a feat like "Work Through It" which would allow characters to 'work through' the pain or coughing fits. I'd appreciate some suggestions on that.

I do like the Plaguetouched idea, I might use that at some later date.