Question: How many BTUs should a grill have?
Answer: While the number of BTUs that a gas grill generates contributes to the maximum heat that a grill can reach it is not the only factor. It is very difficult to determine the heat output of a grill from just the BTU rating. Size, materials, design all play a role in how much heat you are going to get so don't buy a grill simply because it has a high BTU rating. Compare that number to the square inches of primary grilling area to get an idea of how well this grill might heat. As a very general rule of thumb I like to see about 100 BTUs for each square inch, or at least somewhere in that range. For example a grill with 500 square inches and 50,000 BTUs from the main burners probably produces a good amount of heat. If the BTUs where 40,000 under 500 square inches it might not produce enough heat.
Remember that the BTU rating for a grill is the total amount of heat output by all the burners per hour. This is typically measured not by the actual heat output of a grill but by the fuel consumption of the burners. Since propane has a BTU rating of 15,000 BTUs per pound a 30,000 BTU grill would consume 2 pounds per hour. The higher the BTUs the more frequently you will be getting your tank filled.
Gas grill manufacturers are aware that people tend to look at the BTU rating as a sign of power. They can advertise high numbers for a grill that just doesn't get hot and most large grills make a big deal of their BTU number. Manufacturers also try to make sure that their grill can reach a decent temperature. Of course they all have different opinions as to what that temperature should be. I suggest that you not put too much emphasis on the BTU rating for a grill and look instead at the quality of the construction and the reputation of the maker.