I jut had my first successful MO at the PO today. I used an OVGC from Walgreens with just 50 on it so I wasn't stuck with a huge GC. When I called the OVGV number to see if I needed to activate it over phone, it said that it is valid for anything that uses Visa or MasterCard, including money orders. I have a couple cards coming in the mail this week, so I am just making sure that I can actually do this before I try to MS a few thousand.