If you are evaluating VSTS for use by your team, the ability to customize the default development "process" (agile, SCRUM, formal, etc) is a great feature. The "process template" defines the presentation of things like issue forms and checkin rules. For a good intro to process templates in Team System, see Amy Hagstrom's post on Customizing Process Templates.
Heretofore, the only way to tweak your Visual Studio Team System process template was to edit XML pages by hand. Ugh. The times they be a changin'...
New Goo on Gotdotnet
Joel Semeniuk recently released an alpha version of his Process Template Editor for Visual Studio Team System on gotdotnet Workspaces.