Great timing Mauricio, having had a free Mozy account for a while I decided to commit to an unlimited MozyHome account, but thought I'd check in here first and discovered the discount code :-)

If any one else is following this route, you don't get the discount code box if upgrading from Free to Unlimited - my workaround was to uninstall and create a new Unlimited account. The payment page then does have a place for the discount code. I've paid for a year, which means you only pay for 11 months AND get 10% off.

Thanks M!