This is vague, but I heard on the radio yesterday that a researcher from some university is preparing to market an over-the-counter genetic test for the A1 "addictive personality" allele which is strongly linked to alcoholism. There is little doubt left that alcoholism and other addictive traits have a genetic component, and once there's a cheap and easy test to determine which people have the genes, how will that affect society?
Employers and insurers will obviously have strong incentives to avoid people with a high likelyhood of becoming alcoholics, but what if these addictive personality types can also become "workaholics"? Maybe not so bad for employers.
Even the dating game could be changed. Requests for STD tests are pretty common, but what if a potential mate asked you to have a DNA test before committing? Would your desire for a relationship with a person be affected if you found out that he had the addictive personality gene? If I found out that my child was dating someone with an addictive personality I would certainly warn her away from that person.
But then, genes aren't destiny. I believe in free will, and I'm sure there are more people with the gene who aren't alcoholics than who are. It's probably irrational for individuals to make any decisions about their friends or family based on genetics, and I doubt I'd hold anyone's genes against them in the face of contrary personal experience with the person. But when dealing with huge, statistically valid samples (like the government and corporations do) it could be completely rational to discriminate.
Finally, how might society change if people with "addictive personalities" couldn't find mates? The gene must be useful to the system or it would have died off a long time ago. Alcoholism and the like are terrible, but I don't know if a society without the A1 allele would be nearly as dynamic and interesting.