I think one of the greatest challenges for a project manager is to have a realistic view of how much time team members can really spend on their scheduled tasks. Unplanned activities can put a big dent in projects leading to all sorts of fire fighting; either towards the end of a milestone when the project status is under intense scrutiny or on a more regular basis if the project schedule is being monitored on a regular basis. This is definitely an issue for strongly milestone driven projects; especially for fixed bid projects where the scope and the time are tightly controlled.
I have seen some interesting techniques being employed by project managers to address this issue; especially when using tools like Project and Project Server. For example, only sixty percent of the users’ time is deemed as available for project work. Or all the unplanned activities are tracked in a separate project (requiring the project manager and or the individual team member to be diligent about keeping that project up to date on a regular basis) to determine over all resource utilization and demand. I am sure that there are a number of other techniques used by project managers to keep their schedules in control
So, fellow project managers, if you have any favourite best practices, techniques or processes that allow you to reign in your project schedules, I'd love to hear about them. You can send me an email at ameyab at microsoft dot com or post your comments.