Wouldn't it be easier to ban putting HIPAA protected information into a PowerPoint? We don't ban telephones just because an employee can read patient records over the phone.
PowerPoint should be banned for other reasons, we're just looking for an excuse. :)
Of course putting ePHI in PowerPoint presentations should be against policy. The thing is, when it does happen, it's almost always inadvertent. Unfortunately, the "oops, my bad" defense isn't valid against violations of the HIPAA privacy rule.