Are you getting a persistent message in the lower-left side that says "Unable to connect to Sprintly?"
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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/