What did you use it on? What bugs were you trying to control? What
concentration did you use it at? I found that Neem 1) repels cucumber
beetles and flea beetles for about four days. and 2) It actually stops
the spread of powdery mildew on squash - at least so far.

I used it on tomatoes, peppers, eggplants, string beans, squash, cucumbers
and collards that were infested with 2-spot spider mites and silverwing
whitefly.

I can't comment on the spider mites, as I don't have those here. Did you
spray in the evening, being carefull to get the underside of the leaves?
I've heard that is the best way to get whiteflys. If you just sprayed the
tops of the leaves, it might not do much to whiteflys.