Well I guess I'll break my cherry here!
My opionions for what they are worth:
Insulin is only usefull to those that have been at it for a while and juice no longer does the trick. All others can get big just using juice and it is much safer. Most of the lifters i have spoke to or heard from dont know shit about insulin and that to me is scary because of insulins fast acting nature.
As far as making you fat, it can indirectly cause fat gain as the liver stores fat based on what the insulin level is and a few other factors. Most of you are young however and shouldnt have a prob gaining fat with insulin.
To sum it all up, My bitch is that it has a narrow margin of error and I have a few friends that are now insulin dependent after years of use. The sad part is these guys sucked as bodybuilders and thought insulin would give them an edge. All it did is make the slightly bigger but still shitty bodybuilders and now diabetics. But go ahead use it and see that you wont place any better or break any records because of it.