Quick tip for those that use the Official Facebook app and Don't have working notifications:
Not bothered to search if this has been posted yet...
Notifications have never worked on my facebook app, except friend requests on rare moments...
Firstly, you will need a blackberry or the blackberry simulator and mde email package from the blackberry dev site.
If you have access to a blackberry, log into your facebook account through its facebook app, enable notifications then log out. You can use a friends BB, just remember to clear your details afterwards...
Log onto Facebook on your PC/Mac, goto Account Settings (next to Log Out option).
Click Apps
You should see "Facebook for Blackberry Smartphones", if not, repeat the first step.
Now on your android, goto Manage Applications/Facebook and clear data etc...
Open the Facebook app and log in, goto the settings and make sure Notifications are enabled and thats it, job done, you can even set the retrieval time to none if you dont use the widget.
If you dont have a BB, then you need to download the BB simulator from the BB Dev site plus the MDE email package, 177mb and 45mb respectivly.
Install both then run the sim and use as if it were an actual BB as above...
Did this via the simulator lastnight and it works a treat
Full link here:
http://www.androidnz.net/2011/11/how-to-enable-push-notifications-in.html