I know the DivaCup people say that you shouldn't use hydrogen peroxide or vinegar on your cup; they also advocate boiling for only 2-5 minutes (which might lead one to believe that boiling for longer periods of time is harmful).
Personally, I'm inclined to believe this is all bunk; I've had my cup for two years, have soaked it repeatedly in vinegar-and-water and peroxide-and-water solutions, and have boiled it often (sometimes several times per cycle!) for 10-20 minutes, and have never noticed any problems with the structural integrity of the cup.
But then again, just because I've never witnessed it doesn't mean it's impossible. I know people have experienced general deterioration of silicone cups before...so I guess my question is, did you have a silicone cup which deteriorated, and you believe that it was caused by the use of vinegar and/or peroxide and/or excessive boiling? Comments on cup deterioration attributed to other causes are welcome, as well.
Finally, people who have used any of these methods without any negative effects on the cup are welcome to comment, too.