These changes were part of system enhancements rolled out in the fall of 2010.
DVC hasn't gone out of its way to publicize them but the ability has been discussed on DVC sites/forums.
Basically they can split any trip into multiple segments with each segment having different dining options tied to it. All of the segments are still linked to a single master reservation so there is no need to check in multiple times, just one set of room keys, etc.
Biggest thing to be aware of is that credits are supposed to be tied to the nights for which you buy them. If you buy the Deluxe Dining Plan for a Monday night, you only have Monday and Tuesday to use the credits. Looks like another poster said some of the credits carried over but I wouldn't bet on that always happening--technically it shouldn't.
If you want to attach different dining plans to portions of the stay, it is best to mention this when the reservation is first secured. Member Services needs to establish those individual segments in their computer system. If you are holding a 7 night reservation and want to purchase one dining plan for the first 3 nights and another dining plan for the other 4, they effectively need to CANCEL the entire reservation and re-book accordingly. Some MS reps will tell you that there is a chance of the room being lost while the cancellation/rebooking is happening. Personally I think the odds are pretty remote and apparently they can get a manager involved to further minimize the risk.
But again, if you know you want different dining plans for those 3/4 nights, tell the MS rep right when you book and they can create the separate segments right away.
Can't help you with the mug question. The mug is only part of the quick service dining plan so if you don't have that until the last day of the trip...