If the audience notices it, it's probably a train wreck.If the audience notices mistakes, then it's a problem.
I actually played in a band about 8 years ago where everyone was on the same page. We rehearsed ad nauseum, but when we hit the stage we were so prepared that all we had to think about was making music. You NEVER wondered if someone was going to play a wrong chord, or miss a change, intro or ending. You could just about count the mistakes the whole band made in a whole night on one hand.