I found that it boosted my test levels (by how I felt), but it more than likely just keeps it at an optimal level. I wouldn't go as far as to say that it actually increases it over what your normal body level would be. But MrZap is correct in that it helps you sleep. I make my own, you can check one of my other posts to a ZMA article for a good link. Also the SCIFIT brand is good prices, something like 30 bucks for a 45-60 day supply (not sure on the specifics).
If you take it, make sure you take it on an empty stomach, with no Calcium products near the time you take it as Calcium hurts the absorbtion of Zinc. Also if you make your own, make sure you are using Zinc Asparate and Magnesium Aspartate.
I take it at night and about 1-2 hours later you get a little foggy headed if you don't try to goto bed, and you get some weird ass dreams on it.
As for effectiveness, since I have been taking it I have maintained most of my strength gains while dieting and doing alot more cardio than lifting. Take it for whats its worth, you might try it if you order it off the net for pretty cheap. PS I've read somewhere that you don't really see results untill you take it for like 2 weeks, but Im not sure if that is completely true.