I read somewhere that niacin can be used as an effective pre-workout fat burner by flushing out the fat in your blood that is released when you work out. Hear about this at all?
No I haven't but I don't see why dilating your capillaries could do any harm.
actually, being that niacin decrease fat oxidation of adipose tissue (and thereby decreasing VLDL), it could theoretically decrease the effectiveness of a workout on fat burning.
This, of course, is based upon its physiological action, rather than experience or any studies I have read on this specific subject.