On February 13 the Eighth Circuit joined several other courts of appeal (e.g., 2nd, 5th, 7th, 9th) in ruling that in Americans with Disabilities Act (ADA) cases where an employer argues a job applicant would pose a "direct threat" to their own safety or the safety of others, the employer has the burden of proof. The case is EEOC v. Wal-Mart.
You may remember this issue from when it made headlines in 2002 in the Chevron v. Echazabal case. In that case the U.S. Supreme Court was looking at whether the EEOC regulation that allows the direct threat defense was in conflict with the ADA; the court decided it was not. (By the way, although Chevron won that round, they actually failed to prevail when the case went back down to the 9th circuit).
In the current case, the court ruled that Wal-Mart failed to show that with reasonable accommodation the plaintiff, who has cerebral palsy, would still pose a direct threat. (Primarily relying on testimony from Wal-Mart's expert witness)
What's the upshot? If you're going to deny someone a job based on a disability, tread VERY lightly. Give the person the opportunity to show how they would perform the (well documented) essential functions of the job, with or without reasonable accommodation. And don't assume the "direct threat" defense is a slam dunk; courts are making very clear that it is not. Those types of decisions need to be based on clear medical evidence (see section (r) at the bottom of this page).
More details regarding this type of case can be found in several places, including here.