Due to the high number of missing comment e-mails lately (and also historically over time), I suggest we add a bit to FAQ 62 which specifically states that comment e-mails are not guaranteed, and they should not be relied on as the only method of reading comments.
Proposed text, changes marked:
If you have selected the option to receive comment e-mail notifications, but are still not receiving them, or are only receiving some, see http://www.livejournal.com/support/faqbrowse.bml?faqid=115 for information on why this problem may occur and how to resolve it. Also, due to the nature of e-mail communication, comment notification e-mails are not guaranteed to arrive for every comment you receive or post, and are provided as a courtesy feature only. You should not rely on comment e-mails as your only method of reading or discovering new comments.