I am a psychiatrist… I have heard one (and only one!) of my many chronically drug abusing patients claim that she used to sell her lithium pills to people who would snort it to somehow augment their crack high. Based on this one unreliable report, I am not willing to assume that this bizarre practice is actually widespread.
I would be worried about toxicity…lithium is quite easy to overdose fatally on, or at least end up needing lifelong dialysis or a kidney transplant. Take only as prescribed, kids!