Hi Laura,
Prefixing milestones (eg 01 Planning, 02 Design, etc.) is the simplest approach I've found to group and sort large amounts of task information across disparate projects.
Where other options such as Task Name, Task Number and even custom data could be used, they've all disappointed me as (for one good reason or another) they change, move, or become missing over time, yeilding unorganized results. In contrast, milestones can be assigned to different tasks (and even better: template tasks) to give a holistic view of similar processes across a variety of project types.
I've forgotten if there is an ordinal Milestone order -- if so, perhaps you could group first by that and then the milestone name -- but practically speaking, exposing the prefix is easier and logical enough to explain.
As for an illustration of what you can then do using the prefix convention, I invite you to read my "http://store.atappstore.com/2010/05/one-chart-to-rule-them-all/">One Chart To Rule Them All blog post, which fans of Lean Manufacturing will quickly recognize.
Regards,
Doug
