Personally I feel its about as worthless (or worth while- depending how you look at it) as HMB.
HMB was shown in studies to help untrained athletes with no prior experience in excercise, nutrition, or what have you.
L-Arginine is in my opinion the same way- works in untrained people who eat junk and do not know what "1g protein per 1 pound bodyweight" means.
If you look at you protein powders ingredients, some of them will give you 3-5g of Arginine per shake!! Especially if you make 30-50g shakes. So if you are getting your 3 protein shakes per day that means you should already have your 10g of Arginine. So why waste your money on huge horse pills to get another 10g? its not going to do jack.
On a side note: I DO like how it gives me rock-hard (about to explode) erections though!! at least 5g one hour prior to intimacy rocks!! Feel like I am a horny 18 year old all over again. (and no way I am drinking a big protein shake before THAT type of excercise)