Same problem here (plus drivemount applet do not appear when notifications are not working).
Between logins, if I switch to VT and log with my user, I can see 2 processes remaining from my last gdm session :
bonobo-activation-server and evolution-data-server
If I kill evolution-data-server, then bonobo-activation-server stops and notifications work again in next gdm login.
If I do not kill those processes, notifications do not work in next gdm login.
Same problem here (plus drivemount applet do not appear when notifications are not working).
Between logins, if I switch to VT and log with my user, I can see 2 processes remaining from my last gdm session : activation- server and evolution- data-server data-server, then bonobo- activation- server stops and notifications work again in next gdm login.
bonobo-
If I kill evolution-
If I do not kill those processes, notifications do not work in next gdm login.