I used to take it all the time, noticing that it was a key supplement in one of Randy Cotoure's expensive pills. At the time I was taking it I took it as a pre-gym regiment. Maca, Green Tea pills, and 1 kava pill. Back then I thought that this little cocktail made me more loose and aggressive but as I backed off on supplements I think it was just the green tea pills at work.
I noticed very little benefit from it possibly even just a placebo effect. The theory is that it's supposed to boost your testosterone levels but from what I read t levels and blood flow for an erection (another use for the supplement) aren't directly related. I found very little in the way of substantial studies to back the claims of Maca so I kind of just slowly stopped taking it.
I didn't notice any negative side effects though, so it wouldn't hurt to give it a shot. I have half a bottle left of the stuff so I just might take it again just for the hell of it.