Are you getting a persistent message in the lower-left side that says "Unable to connect to Sprintly?"
It's likely your network or firewall is blocking Pusher; the web service we use for notifications.
You can test your network connection and firewall settings here:
http://test.pusher.com/ — That is a test to see if you can access Pusher.
There's another option here: http://pusher-diagnostics.herokuapp.com/