Instead of building long elevators reaching to the top of your hotel, build many small ones reaching 5-10 floors!! This way the people in the mid don't have to wait until nobody above / below them blocks the elevator, but can run to their short one and go where they want.
Another bug - if you get depth of greater then 1000$ (I bough furniture in expectation of the coming indie-day), the game collapses when you step back over the 1000$-mark; it even shoots my whole Firefox.