The title of this play, in Shakespeare's time, would have been pronounced Much ado about Noting. This idea of Noting is a central theme of the play. People "note" or listen to everything that happens around them, and are influenced by it whether they should be or not. In addition, people make "note" of things to others, and every note is influenced by a person's own beliefs and biases.
The watchmen are the best example, because they don't understand how important their capture is. They have noted, or overheard, the confession of betrayal, but they are unaware of its implications, and therefore do not make the presentation of information to Leonato in time. In addition, they are so poor at conveying information, such bad communicators, and so biased by the actions of the "criminals" they have captured, that their first communication is not fully understood by Leonato. The watchmen don't put forth the most important information, and Leonato, annoyed by their ridiculous speech, dismisses them.
Beatrice and Benedick are tricked into "noting" by their friends. They are tricked into believing that the other has confessed love. They allow themselves to be influenced by this because it is what they both want, therefore they are biased towards the information they overhear. Their happiness is, in part, brought about by "noting".