Well, this
Best Buy deal -- $150 for a $150 BBY GC + $15 coupon, which you'd take in store to buy $165 in Disney GCs -- saves 9%. If you have the cashier scan your Shopkicks app when paying, you'll usually get another 0.8% worth in "kicks" that you can eventually redeem for Best Buy or Target GCs, which you'll turn into Disney GCs. Ebates now offers a 1% cash back in-store coupon for Best Buy, but I haven't tried to see if it applies to GCs.
This isn't the best deal, however, because like
@StuckInKS posted, you can get a base savings of 5% on Disney GCs from Target using the REDcard, or buying Disney GCs already discounted ~5% from Sam's Club or BJs -- and depending on what credit card you have, get another 5% cash back if the rotating bonus category that quarter is for warehouse clubs. All without the worry of converting one store's GC for Disney GCs. ~10% savings is still nice, especially if you don't have time to wait for better deals.
I took advantage of this deal because I'm a bit depleted of Disney GCs, and I have a deposit that I need to make soon that I refuse to pay "full price" on.