I was having a problem where I was the only account that would show up in the "Assign To" dialog.
All the developers in our team were Contributors via a security group.
I found that after manually adding them under TeamProjectName/Team Mambers in Team Explorer, AND restarting Visual Studio, they now show up.
Just incase anyone else is having this problem I wanted to post this here.
I'm not sure WHY our users don't show up under Team Members when I have "Contributors" selected as the default list to show. I'm guessing that because we assigned the development group to Contributors and not each individual account that
causes the problem.