Once you have logged in and chosen your selected project (upper right corner of the screen, white dropdown underneath the words "Current Project") you can view the members of the project by clicking on the 'User List' link on the left side of the screen near the top.

This gives the "normal user" view of the user list.

If you are a project administrator, though you can also view everyone that has been invited to the project but not yet accepted the invitation. To do this, make sure that the current project is the desired one (if you are an administrator of the project the project name will be followed by [ADMIN]), and click on the Utilities link on the left hand columm of the screen. The resulting page will have a Current Project box with Administrator Options. Clicking on the 'Invite users to the current project' link will show a list of current project members and, if you scroll down, the list of users who have been invited but haven't yet accepted the invitation.