If we only went to Disney once a year, I'd buy new mugs every time. But we went 4 times in less than a year. In December 2006 we bought the ASMO-specific mugs and never reused them. But we used the same mugs for our July, October and December trips this year. Sorry, I'm not buying three times the exact same mugs, especially since we never use them at home.
Since it was our last trip of 2007, we left the mugs in our room at the end of our stay. We'll buy new ones in 2008.
Considering our July+October+December trips put about 12K in Mickey's pocket, I really doubt they care if we bring our mugs to drink the soda they don't pay for.
If they do, they're welcome to send me a bill.