Like many of you I am a heavier biker and have killed off the rear wheels of several cheap x-mart bikes. I bought a Fuji Supreme in February and since then have put about 350 mi. on it. When I bought it the LBS owner commented that her tandem had the same rear wheel and they rode with about 340 lbs on it. Its got the stock 36 spoke wheels.
I just broke my first spoke on the rear wheel last week. I'm hoping that it will not be the first of a string of breaks. I do not ride that hard (no curb jumping, mostly paved trails and roads, etc.) Probably the biggest strain on the wheels in the first mile of the bike path I use which is unpaved and full of loose stone and gravel and gulleys. Heavy rains and no maintenance have left that section of trail rutted and in bad shape. My guess is that bad trail + heavy biker = premature spoke death.
Hopefully as I lose weight things will get easier on the wheels. My LBS fixed it for me for $16 so I'm happy and will be back to my normal long ride next week.