The "Holy Grail" (Karl Groves) easy to incorporate 'help' text!
<label for="date">Date: <input type="text" size="30" id="date"><br />
in form of mm/dd/yyyy
</label>
Will cause Voiceover and Safari to speak <label> twice. Voiceover/Safari only works properly with Explict labeling. - Scott O'hara
Explicit labels are the easiest way to ensure that most user agents can associate form prompts with the correct control.
<label for="date">Date: </label>
<input type="text" size="30" id="date" />
Implicit labels are legal according to the spec.
<label>Date: <input type="text" size="30"></label>