There was this option available "Do not remind again" but then that option disappeared lately. Now there is no way to stop the nags for session in progress.
Please bring that option back. It is better to at least have the option for the running session if not permanently stop the nags. I thought the nags were randomly showing up every five minutes but that is not the case. You move to some other window and come back to GoToMeeting, the nag shows up. Repeat this a hundred times and you will get nagged a hundred times.
Other than this nag, GoToMeeting works flawless. Crisp clear sound and easy to share screen. Love GoToMeeting!