This is what I was able to find on zyngas site
"Resolving Push Notification Failures
Kevin Kelly Jun-17 2010
If you are not getting push notifications, first check our Announcements pages to see if there are any known Notifications outages.
Also note that jailbroken devices may have problems with push notification and users of affected devices will need to resolve that issue before notifications will work with WWF.
If an account has been logged into with the paid app then notifications will no longer be sent to the free app for that account.
If there are no outages (and neither of the other two situations described apply) then make sure that notifications are enabled for the app on your device:
Go to your device's settings
Then go to Notifications
Make sure the main Notifications setting is ON
On the list below, tap each GWF app and make sure each of Sounds, Alerts and Badges is ON
If after checking each of these items you are still not receiving Push Notifications then take the following steps:
switch the main Notifications setting to OFF.
Reboot your iPhone (or iPod / iPad)"