Often a milestone is targeted at a particular date, but it is not easy to see whether targeted tasks are on schedule for that date.
To work around this, Ubuntu and Linaro teams both use burndown charts hosted outside of Launchpad. <http://status.ubuntu.com> <http://status.linaro.org/> Unfortunately, this causes a lot of bureaucracy in copying or linking issues from bug reports to blueprints. And to the extent that developers don't get around to doing that copying or linking, then bug fixes are implicitly deprioritized in favor of features, lowering the software's quality.
This could be fixed in Launchpad by providing a Burndown view of bug reports, as a toggle with the existing List view.
Implementing this would require first implementing a bug listing for milestones.