AMD's weight limit is 300 grams. But you're right, practically half the CPU coolers out there, maybe more than half, are over 300 grams. But you should still be okay with something up to 500 grams as long as you don't have to move your computer. The reason why weight and crushing the CPU core is a problem is that a lot of people move their computer around a lot for LAN parties. Of course you can also crush it while installing but if you're careful enough this should be no problem at all.
Because of the weight problem, some people buy what are called "shims". These are protective masks that go on top of a processor to prevent crushing. Shims will probably make your CPU a little hotter though because they suffocate the CPU core a little. But many people really like shims and if you move your computer around a lot, they're a must.
Anyway, if your computer sits in one place all day long, don't worry about weight. I'd really worry if the weight got to over 500 grams but otherwise weight shouldn't be a problem if you're careful when installing the cooler. As a precaution, the Swiftech model you're thinking of buying is over 500 grams, and I believe it is one of the heaviest coolers out there.
My personal preference for coolers is either the noisecontrol silverado (about 400-450 grams) or the volcano 7+ (a little less than the silverado), or alternatively buying one of those noisy delta fans and using a zalman fanmate to reduce the fan speed. Many people report success in being able to remove the whine of the deltas (ok, more like the scream) when they reduce fanspeed. Fanmates are really easy to use, and I just bought a bunch for my old athlon slot a for really cheap.