A lot of users have problems on OS X Yosemite 10.10 with the Notification Center, it doesn’t store the settings correctly. All custom settings are gone after a restart and you have to configure it again and again… Because I don’t want to loose my precious time I found a easy solution.
Just open the Terminal application (you could start the application with Spotlight -> Terminal) and move the NotificationCenter folder (located in your current users
~/Libaray/Application Support/) to your Desktop, just to keep it as backup (I never needed it!)
mv ~/Library/Application\ Support/NotificationCenter ~/Desktop/
Now go to the DARWIN_USER_DIR folder, delete the settings for the Notification Center and kill the Notification Center processes.
cd `getconf DARWIN_USER_DIR` rm -rf com.apple.notificationcenter killall usernoted; killall NotificationCenter
I have had to restart my Mac twice to get this work finally, so just do it also.
Let me know if this could fix your problem too!