I go to WDW 4-6 times a year and have used DME since the very first week it was in existence (yeah, I was one of the original guinea pigs

). It's a great service and I have never had a problem or complaint. On average it takes maybe 75 minutes from the time the plane lands to get to your resort. (Some trips have been shorter, but it's never taken over 90 minutes, even when we were the last stop and some people had alot of luggage they had brought on to unload--don't know why people do that

). As far as how long the luggage takes, we've never had a problem there either. I usually arrive at MCO around 9:30am and after checking in, go straight to the parks to eat lunch. My bags have always been waiting in the room for me when I get back that night. Last Dec, I arrived at CSR about 10:45 and decided to walk around the resort taking pictures. Maybe 45 minutes later as I was headed back to my room, I saw one of those carts with my bright green duffel on the back. I caught the CM as he was walking back from delivering bags to another room, told him the bag was mine, and would save him a trip to my room. He told me he couldn't give it to me, even with ID. He said he was required to deliver it to the room, but to hop on and he'd take me there. When we got to the room, I again tried to take my bag and he wouldn't let me, telling me he was required to scan his key to show he had delivered it inside the room. He scanned his key and punched some info into a little machine he had and I followed him into the room, where he finally released the bag to me. I know tips are included for luggage delivery, but felt funny not giving him anything, so offered him a couple of bucks, which he told me he wasn't allowed to take, since tips are included as part of the luggage delivery. Anyway, my point is, I know for that trip at least that my luggage was delivered
very promptly. I've never had a problem with lost luggage. Since you tell them when you check in at the DME podium how many bags you checked, if they don't find that many, they will immediately know if the airline lost a bag and will start them looking for it immediately.
DME is a great service. We love them. In fact, I used them last Sept and again in Nov/Dec and will be using them again in Feb, May, Sept, and Oct/Nov.