My experience is similar to Iron Queen's. I used 10-20mg per day starting 6 weeks out (when I'm down to ~12%bf or less) from comp. I also have tried it when I wasn't lean and it didn't do anything for me. I think the extra estrogen churned out from large adipose stores may swamp the effects of Nolvadex, but as the adipose reserves go down you produce less peripheral estrogen and Nolvadex may have a better chance at competing at the receptor level. Nolvadex is also picky as to how it acts at diff receptors, and can have a negative impact on triglycerides. This may be why postmenopausal women given Nolvadex are likely to GAIN fat. Nolvadex can also be estrogenic at some receptors, and it may be that different women have varying distribution of these receptors in their thighs and butts.
Whatever the theory, in practice many women find it works OK once they've already lost most of the fat, and is good to help get rid of the last of that stubborn lower bodyfat. But if you're post menopausal, not dieting and not already lean then you may gain fat.
Arimidex on the other hand, will inhibit the production of a large percentage of estrogen and should 'in theory' work more consistantly in women looking to block the gain of fat from estrogen. I haven't tried Arimidex. I'm wondering if Wilson6 has any client info on this supplement?