I second Power Player's comment. I'd also like to add that often times it's not necessarily the swing weight that is most troublesome, but improper balance. If you're used to 7 to 10 points head light, and you throw 5 grams of lead in the hoop, you've just made your frame even balanced or head heavy.
That, more than anything (even a high swingweight) will throw you off.
For instance, with my Prestige Pro, if I take the stock frame and add anything from 2 to 6 grams in the hoop, with no other weight anywhere else, I can't even play a full match with it. Everything is out, long, wide, and i get tired. I have 0 success with it as an even balanced or head heavy racquet.
But if I properly balance it, it's like buttah. Right now I have 10 grams at noon and 10 grams in the butt cap and it's the best frame i've ever used. Without that extra weight, 80% of my shots land on the service line. Now with the weight, only 30% of my shots land on the service line, and some of that % is because I wanted it to be short for some reason. Because it's still 7 points head light, i really don't notice the weight at all.