There is not a report in QC, but you can have your DBA run a SQL against the master qc database/schema (qcsiteadmin_db) to get the information.

SELECT
USER_NAME,
PROJECT_NAME
FROM
td.USERS_PROJECTS
INNER JOIN td.USERS ON USERS_PROJECTS.USER_ID=USERS.USER_ID
INNER JOIN td.PROJECTS ON USERS_PROJECTS.PROJECT_ID=PROJECTS.PROJECT_ID

![alt text][1]

[1]: /upfiles/USERS_by_Project.jpg