I've only made one that I know of... and I knew it was wrong the minute the patient had swallowed the last pill.

It's an experience I will never forget. Thankfully, nothing tragic resulted from this error. I have absolutely no difficulties reporting such things. In this case, the facility I was working in, made a policy not to have the same named people in the same room. Evelyn Smith & Evelyn Jones or Wilma Smith and Bertha Smith.
The facility I've been working at for the past 6 years, just opened a new facility in February 2006 and all the rooms are private. We've also join the Pyxis generation.