In the Google Apps connector in Crowd 1.5:

• When you sign out of Google Apps, you will also be signed out of Crowd and all Crowd-connected applications. This is the usual SSO behaviour.
• But when you sign out of Crowd, you will remain logged in to Google Apps even though you will be logged out of other Crowd-connected applications. (Reason: Google does not rely on a cookie, so there is no easy way for Crowd to tell Google you have signed out.)

It would be nice if Crowd could support single sign-out of Google Apps.