Ask about the return vouchers when you get to the DME counter at MCO upon arrival.
As to the OP's problem of the wrong date on the return voucher, certainly you should check it out at the DME counter when you arrive at MCO, but it's really nothing to worry about. The same thing happened to me. I received my DMe booklet on the day before my trip. I noticed that it listed my arrival day correctly but it listed my departure day as the following day! Naturally, I was concerned, and since I was leaving on May 8, the 4th day of DME, I was expecting a MAJOR screw-up even though I've been a big cheerleader

for DME since it was first announced).
I called DME and they had my correct flight information in the computer even though it was misprinted in my packet (I know they had it right because the CM read it to me rather than my telling him and asking him to confirm it). Everything went well, no problems, I loved DME and I know it's not guaranteed but I sure hope it's still around (and FREE) when I return in 2007 or 2008.
Another aside: some time during my May 8 - 14 vacation I misplaced my DME return bus vouchers. The driver, who's a Mears employee and not a DIsney CM, behaved in a very Disney-like manner. He smiled and told me not to worry, and said my name was on his list and he would let my family board as long as I (only me, not everyone in my party of 6) could show him ID as well as anything official from Disney with my name on it; I had lots, such as my original WDTC hotel voucher, my WDTC guest itinerary, my unused DME tags still in my DME booklet, etc. Funny thing: While typing this I just looked through my clear plastic WDTC travel folder thing and I JUST FOUND MY DME RETURN BUS VOUCHERS!!! Boy, that was a good vacation -- I couldn't even find a piece of paper that was right under my nose!
-- Eric
