Just how important are recommendation letters?

I've heard different opinions on this. On one hand, some have told me that as long as the letters are not bad or ridiculously good, they won't make too much of a difference. On the other hand, some have said that recs are the second most important component of the application, aside from work experience.

Is the truth somewhere in the middle? I think my letters will be good, and i've given them guidelines, but it's always nerve wrecking because ultimately you don't know exactly what they are going to say. You sort of need to have "faith" that they will do a good job of vouching for you.