Allows specifying "canned responses"
I used to use the (old / classic) SourceForge.net trackers a lot (out of lack of alternatives, not of choice ;-). Overall, Redmine is a big win compared to it, but there are a handful of features I am missing.
One is the ability to specify "canned responses". That is, one could specify a set of predefined response texts. Then, instead of writing a new comment on an issue, one could simply add one of those canned responses to an issue by selecting it from a popup.
The idea is that many workflows require certain responses over and over again. For example: "Thank you very much for you report. However, in order to be able to process it effectively, we need further information. Please tell us the exact version of FOOBAR, the operating system on your computer (Windows, Mac OS X, Linux, ...) and ..."
Another example: "This issue is currently awaiting feedback. If we don't hear back from you within 14 days from now, this issue will automatically be closed."
Providing such canned responses has multiple advantages. One, it saves time. Two, it allows pre-crafting polite and yet succinct replies. (I found that if developers handle requests, as is often the case on open source projects, sometimes replies lack in politeness simply because after looking at the tenth report in a row which is ignoring the bug submission instructions, you tend to get a bit upset... esp. if you do this all in your spare time. A pre-written text helps avoid letting the user feel that annoyance).
Anyway, I hope it is clear why I consider this useful.
I actually think that in Redmine, one could provide a nicer UI for this than SF.net did. E.g. it would be nice if upon selecting such a canned response, it would simply be inserted into the text field, so that I can edit it before submitting it. Also note that canned responses could potentially do more than just predefining a response text; they could also include other status changes. But to me, that would be extra sugar, not a requirement.