Great experience with these guys personally, straight from the email:
Share The Love And Be REWARDED!
You're having a good time - right? Share the love and give the gift of space to a friend, family member, colleague, or nemesis. They score $75 off their first TAXIBOX booking, and we'll send you a $50 gift card of your choice for sharing the love!
These codes are different from the standard ones ("Friend-of-X"), instead ending with "PAL".
Highly recommend these guys. They were great for my recent move!