How long can I keep it? I made 2 batches and didn't use it all. Do I need to refrigerate it? How long will it keep, either way?
Oh, and how long do we have to practice before we get the smoothing down!?!?!?

Hi, you can keep it for months. You even can freeze it. I have done it, and didn't have any problem at all.

I don't use buttercream to cover my cakes. But " Practice Makes Perfect"

I only use Sugarshack's buttercream and wouldn't dream of using anything else. I have kept mine for up to 2 months but you can probably keep it longer. As for the smoothing, practice makes perfect. If you use Sugarshack's buttercream, it will crust within seconds and then use the Viva paper towel method. It will smooth out as smooth as fondant.