I came here with this same question.  I never saw the Comments section.  I went back through check out to see why.
 
	On the page with the notes section, Paypal AUTOMATICALLY scrolls to the bottom of the page to the Send Payment Now button.  I just did it 3 times in a row.
 
	This is what I saw each time.  If you want to put in a note you have to scroll up, which isn't very intuitive.  You'd think the note section would be between the total and the payment button.
 
	 
	 
 
	I hope this helps people out with Paypal's terribly designed Payment page.