I have a ridiculous number of mugs from 1994 on. I've donated or thrown out a lot of duplicates but kept one of each design. Most of them are resort specific mugs, since as a pp mention 2007 started the generic mugs. I have them from most of the resorts Poly, GF, CR, WL, CBR, CSR, Dixie Landings, Port Orleans before it was POFQ, PO Riverside, ASMo, ASMu, BWI, BC, AKL. I have different designs for many resorts, and different styles, such as the short plastic coffee cup ones in blue or pink from CBR (the only resort I know of that had that style), to the taller wider mugs, to the car cup holder styles offered now. I have clear with silver glitter mugs from 1997 stay at Poly I think, they say 25th anniversary. I try to get a Christmas mug with hot chocolate each year at HS and I have quite a few of those.
I don't remember when signs started going up saying mugs were good for length of stay. I know I have plenty from before there were signs, but we bought new mugs because we stayed some place new, there were new designs, etc. We didn't buy any mugs our last trip, I already have 8 of the current design, and we were planning only breakfast at our resort, so we just purchased our drinks. First trip without a mug! It felt weird, but a mug cost more than what I was going to spend on drinks and it was the same old design.
I wish they would go back to resort specific mugs!