Best practices for push notifications in multi user applications?

We're implementing this by Registering the device with APSN, getting the device token and sending this to our server through a ws.

On the server side the device token is only associated with the last logged in user.

New app
User A (first ever user) uses IPAD A
Register with APSN, get token
Send token to our servers through ws
Search for token in db, token is new, store it
assign token to USER A

Next user logs into app
Register with APSN, get token
Send token to our servers through ws
Search for token in db, token exists already
Remove connection to USER A
assign token to USER B

SEND Notification to device WITH USERNAME
if username is logged in show it - else dont

Still not perfect as its sent to home screen first so to ALL users

I think your suggestion is acceptable in a multi-user app. It is much simpler to implement this in the client side, than on the server side. The downside is extra bandwidth wasted to send an unneeded notification. But vast majority of the usage is probably single-user so this may not matter much.

The alternative is to track the logged on users on your server and their current reg_ids. This could be more complicated because A could be logged on on multiple devices, then logs out from device 1, and B logs onto device 1, etc. and your server has to track all of these. So probably another table to track the relationships between 'Logged On Users' to 'Reg Ids'.

If you hate the idea of sending unneeded notifications, go with the server route. If you value Keep-It-Simple principle, go with the client route.