One of the most important characteristics of a racquet is the swing weight, or inertia. This is really the dynamic weight of the racquet and is a measure of power potential, i.e. the higher the swing weight the more power the racquet can produce.
Of course there is a trade-off, and that is maneuverability. If you cross the threshold into massive swing weight, such as 350 and up you are going to be really tired of swinging that thing, unless you are a touring professional and even then that is a big swing weight.
So, without going into a lot of detail I would like to see everyone using a swing weight of not less than 315. If you are not sure what your swing weight is bring your racquets by the shop and I can test them for you. If necessary swing weight can be increased.
Remember, in tennis, weight is your friend. On the racquet that is.