I'm holding 3 ressies right now but on different dates each a month apart. Most likely I will actually go on two of those trips, with the 3rd more uncertain. Each time I booked, the reservation agent acted like they were unaware of the other bookings.
I know people hold 2 or more hotels at WDW for the same time period based on what deals they anticipate might be coming out in the future. Why not? Its your money, disney wants it, just remember to cancel in time.