I used one pair of press on nails for Halloween when I was a kid. I went as Batman, and the store had nails with the Batman symbol on them. About half of them came off within a few hours. But that was the 80's, and things may have changed since then.
To be perfectly honest, I hate fake nails of any kind. They just scream "high maintenance" in a bad way to me. I wouldn't even wear fake nails if I was getting married. I just really don't like them.
BUT I can definitely understand situations like Karren's where they would be the best option.