Nolvadex is used fairly commonly by female competitors looking to shed the last bit of fat on the lower body prior to competition. It does this by blocking the estrogen receptors, thereby preventing estrogen from doing it's job. Since many of the fat deposits on women are estrogen-related, Nolvadex can be effective at eliminating them. Women often use more than is needed. A dose of 10mg/day is effective in most women, though some will go a bit higher. I think a rebound is fairly inevitable when coming off of the the compound. You are blocking the action of a very powerful hormone, and when you stop using the Nolvadex, the effects of estrogen are going to be felt again quickly, including the body fat deposits. Using the lowest effective dose is probably smart in keeping the rebound effect low.
It is important to remember, competitors are using methods like this to look great for a single day (or maybe a few days) out of the year. It isn't something that is safe to stay on permanently, as estrogen is what makes you a woman. Nolvadex will not eliminate fat deposits permanently, though it may be helpful if you are trying to look great for a vacation, competition, etc.