I've booked Groupon hotel deals before and had no problems. If you are concerned about dates, you can always ring the hotel before you buy the groupon for an idea of availability
Cold, you have to purchase the deal BEFORE finding out what dates are available, so probably only some Mondays (except for the August bank holiday) available . :/
Go swimming :p
Hmmmmm... I wonder what I will do on that 1 night in the hotel with the Mrs.