When you choose to Invite Friends to an event, you can:

Enter a name for the Event
Choose the occassion
Choose from groups of Paint Nite friends you have created, or
Choose from Facebook friends.

This way you don't need to remember email addresses.

This requires Paint Nite to to connect to the Facebook app.

After you select the invitees, you can send the invitation.

Based on the occassion selected, a custom invitation will be sent.
The invitation will pop up in Facebook and people can respond. Along with the invitation will be a link to download app, if needed, and sign up for the selected event.

Friends who sign up are added to the event: Girl’s Nite Out

If this is a group of Facebook friends, you can create a new Paint Nite group