Just say no.
I did aluminum nipples once. It's just not worth it. I'm fully convinced that no combination of care, tooling and antisieze will prevent you from rounding them off if you care that your wheel is semi-true and are the least bit un-smooth. It was worse than being married to a ginger. Either one could ruin your day at a moments notice.
The g-sport nipples are most likely tons better, but you're still going to end up galling a few of them eventually to save like two ounces while you're possibly running 27 ounce tires.
If you're already on Kevlar bead tires, some stupid light rims, .8mm thick tubes and titanium spokes, cool. have fun. Otherwise there are less painful ways to save rotational weight.
Read this after my last post above..... You are wrong in the assumption that the G-Sport nipples are the same as regular alloy nipples. Very wrong, in fact. For me, it isn't about them being lighter weight than brass nipples. It is their ability to lace up the wheel with the most tension in the spokes humanly possible. In the words of Adam22........walk with me.......
So one time I wanted to lace up the tightest god damn spoke tension allowed by the force of Joe Rich's dread locks. I used G-Sport nipples with the copper anti seize that comes with Odyssey cranks. I laced the wheel up as tight as I could with my fingers/provided spoke tool. THEN, thanks to the 6mm hex head on the nipples, I used my handy dandy hand held impact drill to finish the job. AHHHH, I can still hear that lovely sound of "TINK TINK TINK TINK" of the impact gun. The wheels were seriously the best wheels I ever built. You couldn't even get one spoke to flex. This was 100% due to using the G-Sport nipples. No other nipple, be it brass or alloy, would have been able to stand up to that.
Spoke tension, bro. Get you some.
I run my shit pretty tight. Empire built my current wheels (I've heard Tom builds pretty tight wheels) then after riding them for about a week I put about another turn and a half into them. I do generally like to make sure they can deflect at least a little though because I'm concerned about deforming the hub shell, or even pulling the flange off completely (I think I've seen a picture of that on here).
I've never used Gsport nipples, so I'm not really trying to say anything good or bad about them. I haven't had too much of an issue with brass nipples, but the one thing they have that both normal alloy and g-sport nipples don't, is that when I do round one off or (in the case of alloys) seize one to a spoke, I can just run around the corner to my shitty LBS and get a new one.
My primary problem with alloy nipples (Gsport or not) is galling. Yes, disciplined use of appropriate thread lubricants can almost completely eliminate that issue; however, it almost never fails that if I'm truing a wheel and round a nipple, when I replace it I forget to lubricate it, then next time I go to true the wheel that nipple is seized. Brass is self lubricating and minimizes that failure mode.
Maybe the G-sport nipples being 7075 minimizes that issue (I'm almost certain 7075 is harder), but it comes back to possibly being more risky then it's worth. Back to my ginger analogy: yes, they are wild as fuck in bed; yes you look like a bad motherfucker being seen with them, but their natural tendency to go thermonuclear and fuck your whole week up makes the cost benefit difficult to justify.
Let me just quantify my whole position really quick; I like straight wheels. I toss my wheels into a stand every time they come off the bike. If you only fuck with your wheels when they get bad enough to become a problem, your mileage may vary.
I am starting to think that I want to try Gsport nipples now though.