The About dialog shows the version of TortoiseCVS itself as well as the CVS client it uses, and the SSH application you have configured.
When invoked in a sandbox, the About dialog shows the version of the CVS server as well.
It also has a Credits... button, which opens another dialog listing the people who have contributed to TortoiseCVS development. If you hold the mouse over a name, a tooltip will show what that person has contributed.