Desert Inn has lockers for your luggage, I think they're like $1 or $1.50 in quarters (they'll make change for you at the front desk). DI&S generally doesn't hold your luggage behind the counter, but I like the locker thing better because there's easy access any time. When we got there too early to check in on our first day, put our stuff in the (big, roomy) locker and came back for it when we could get into our room in the afternoon. Same thing on our last day, we left it in the locker and got it out in time to get on our shuttle.
I have even read that some people who are staying farther along Harbor and taking the shuttle will use DS&I's lockers, and arrange for shuttle pickup there, because it's closer to access than walking back to their own hotel and getting their held luggage from the front desk.
When you check in, they'll tell you where to go for the lockers-- you go out the lobby door and turn left. There is parking along the wall under the overhang, and you walk past the indoor pool. The lockers are in a room on the left just beyond that.
