there is a rather large anti-soy movement out there, based on some studies that are real and relavent, but the conclusions are often poorly used.
what i've found is, through the studies that i've read, is that too much soy isn't good for you. But how much is too much soy? well, it's a crazy amount of soy--like soy is all that you are eating ever. WHen they did the study (on animals no less!), they gave the animals a soy-only diet that consisted of something like 4 times the usual amounts that humans get in a regular diet that includes soy and in vegetarian diets. So, these animals came up sick--well, no wonder.
1. all they ate was soy;
2. they ate more soy than a human would eat anyway (not in quanity, but percentage by mass or weight, you know?); and
3. mice have different nutritional requirements than humans anyway--so their normal healthy diet would look drastically different than ours, so perhaps any human diet would make mice sick (i dunno).
anyway, it's worth looking at, and particularly the human studies, but i am not overly concerned. I get a decent amount of soy each day--say 2 or 3 servings, if that much. I'm sure i'm going to be ok.