In the profile preferences, it would be nice to have more option in terms of the frequency of "Email me my unread inbox messages".
Currently, the shorter possible time window is 3 hours. Personally, I would like to set it as short as possible.
Sometimes one gets really impatient about a question, or one benefits from a nice interaction with a responder who remains online for some time. Refreshing the page say every minute to see if something new came up is obviously not the most efficient way to deal with these situations. An email notification would be much more handy.
Question : Do you see any reason why such additional (shorter) settings could cause problems? Would that be too resource demanding for stack exchange servers?
Personally, I see at least one downside : it could facilitate the use of comments as chatting device, which is something stackechange tries to discourage.