Everytime I have used it has worked well. I always keep some around since I work in a hospital. It's the only over the counter drug I know of that actually goes after the cold bug whereas the many other medicines for the cold only treat the symptoms. I believe they say that a clinical study shows that it reduces the duration by 75% if you take it within 24-48 hours of the onset of your cold.
I'm trying Zicam right now since I feel a cold coming on. I'm using the RapidMelt tablets. They are teh nasty tasting. So far, I'm on number 3 and I swallowed it whole due teh nasty tasting. Then I read the bottle and it says, "Do not swallow whole". I hope I don't explode.