Don't waste your time with UNetbootin.
Been trying to get a bootable USB to test out Linux distros most of the day using UNetbootin but wasn't have much success. Well, the "Answer" was right in front of me all along. Just use Startup Disk Creator in Ubuntu 12.04 to make your "live" USB bootable disk and it'll set persistence and an ext2 partition and everything so that it works like a champ. I'm running with the 8GB SanDisk with Peppermint One on it right now and I could even update everything without running out of room like I was with the USB disks I'd made with UNetbootin. Looks like Ubuntu had the solution all along.LOL.
"Gentlemen, you can't fight in here! This is the War Room!"