If you have Project Server, you can use the project sites feature which includes SharePoint task, issues and risk lists that link to the project schedule.
If you only have SharePoint or some other means of hosting a discussion (Google groups? Outlook public folders?), you could just reference a project name and task in the thread title. Investigate to make sure the system will let you customize the recipient list the way you want so that subscribers don’t get too much e-mail that is irrelevant to them.