I purchased a ticket on United.com and used a $100 gift cert for partial payment with the remainder going on a credit card. I cancelled the reservation 4 hrs later but was told only the CC portion was refundable and not the gift certificate portion. After some complaining they gave me a $100 Travel Cert PIN in lieu of the gift card.

I thought gift cards were the same as cash (at least in California), but closer examination of the 24 refund policy shows that "e-certificates" are excluded. So it was my fault for not reading the policy closer before purchasing the ticket, but the policy seems a little suspect to me.