This New York Times article nicely summarizes the complex issues facing patients considering a genetic test. On one hand, genetic tests can help improve an individual's health care prospects. On the other hand, there is considerable fear that the results from a genetic test could be used in a discriminatory way - resulting in the loss of health insurance, or even one's job.
While there have been few documented cases of actual discrimination by health care insurers or employers, the spectre of discrimination leads many to pay out of pocket for genetic tests and use fake identities to learn of their test results.
Illinois has a state law prohibiting discrimination on the basis of a genetic test, but similar legislation is currently lacking at the national level. A bill to outlaw genetic discrimination, the Genetic Information Non-Discrimination Act (GINA), passed the U.S. House of Representatives in April of 2007 by a vote of 420-3, but has not yet made it to the Senate floor. A legislative summary of the bill can be found here.