I saw this thread and just had to join bluelight so I could put in my two cents...
So, as for shooting in the genitals (at least if you're a male):
Is it a good idea (is shooting in an extremity ever a good idea)? No. Will it ever be considered socially acceptable among junkies? Probably not. Is it a viable option when all your other veins start to go? Absolutely. Do it properly and it won't be much more painful or dangerous than shooting in your forearm. Seriously. Well, okay, you feel the initial pinch/sting of the needle, but it's FAR from unbearable. However, please, PLEASE make sure you register properly; if you miss, it will be quite painful and obviously potentially dangerous. Also, this is a place where it's ESPECIALLY important to use a new needle every time.
Unfortunately, I have poor genetics when it comes to veins. Despite the fact I work out quite often and am in excellent physical shape, I'm not particularly vascular like all of those tall, skinny, teenage white bastards out there. Also, my veins start building scar tissue EXTREMELY quickly. My entire left jugular lasted all of two months before it was tapped out, even with rotations. It's not poor technique, trust me; I'm obsessive-compulsive about that. A large part of it is the tar here in Phoenix. It can get pretty potent, but it's always absolute hell on my veins. Anyway, the large vein on top of my penis is now my regular go-to spot when I can't hit anywhere else. It seems much more resilient to collapsing and sclerosis than my other veins, and it's VERY easy to hit. It's best to do it with a half-erection: this way, the veins are relatively engorged and much, much less likely to roll. Personally, I think doing it with a full erection is a terrible idea, although I've seen several people do this. The reason NOT to do this is because when you have an erection, there's a lot of blood pumping into your veins, but not much leaving them, hence the ability to maintain the hard-on by reducing outward circulation. Also, it's hard enough to get most people to poke themselves in their limp, flaccid dick, so who the HELL would want to do it with a raging hard-on? Not I, at least.
Anyway, I know the majority of you people are completely opposed to the idea, but since I've never seen anybody go into any kind of detail on the process, I figured I'd give my two cents just in case anybody gets curious. Better to be informed, at least.
[Disclaimer! I am not condoning this; always, ALWAYS avoid using the extremities if at all possible, and always use the best technique you're capable of. Unless you're in full-blown WD's, there's absolutely no excuse for being sloppy.
Be safe, everyone.
BTW, this has had absolutely no negative impact on my ability to perform sexually.