Add a time estimate field to issues

A time estimate field in the issues would allow Agile processes.

Simply being able to record a time estimate would be enough, but getting total time estimates by milestone would be great, and being able to see a burndown chart (preferably embeddable in a wiki page) would be spectacular.

There is often a temptation to add "total time" and "percent complete" etc, but a single field "time remaining" is enough.