Here are the review guidelines i found in the FAQ section:

Stay on the topic of the submission and do not make personal remarks or insults towards the author. This is a big offense. Telling artists "You suck!", "You should go kill yourself!", "You are gay!" etc., will get you banned and you may lose your account. Without our contributors Newgrounds wouldn't be what it is, so we take seriously any insults directed at them by reviewers.

Do not post TONS and TONS of crappy reviews just to get high in the rankings. If we catch someone doing this we will delete all their reviews - wouldn't that be a pain in the ass? Take your time and write a sincere review for every movie you wish to critique. Make sure your review is relative to the submission. Reviews that are found to offer no benefit to the author may be deleted.

Do not use the review space for the purpose of promoting things. Stick to reviewing the movies - we don't want to hear about how great your website is. Also, posting links to websites that reward you for sending hits is prohibited; we will delete your account for the first offense with no warning. Posting unrelated links is also prohibited and will result in a ban.

Do not flood the review title or body. Examples would be long strings of characters or words with no breaks or repeating words or phrases over and over. Do not submit images made from text and characters, as this will also get you banned.

Do not use reviews to express your feelings that the entry should be BLAMMED. If you post "BLAM this" or something similar you will be banned. Use the review option to tell the author how they can improve their work.

Do not use the review field to address other user's reviews you didn't agree with. You are to be reviewing the submission, not other people's reviews.

If you believe an entry is stolen, do not comment about it in your review. If you are wrong, you may convince other users that the entry is stolen and you may cause a legitimate entry to receive an unfairly low score, or have the whistle blown on it. Use the whistle option, if available, to flag the entry as stolen when you believe that is the case. If there is no whistle option available (the entry is no longer under judgment) contact Wade with as many details as you can about the stolen Flash and where you think it was stolen from.

If you think a submission doesn't belong on the front page of the site or shouldn't be featured in special sections of the site, keep it to yourself. The submissions on the front page and in special sections of the site are put there by our staff, not by the author. Keep your focus on how the person who submitted might improve their work.

A couple of days ago i wrote what i thought was a rather honest review. I didn't insult the author, i didn't post loads of crap reviews, i didn't promote anything, i didn't flood the body of the review box, at no point did i say it should be blammed, i never said anybody elses reviews were crap, i didn't say i believed it was stolen, and i didn't say it shouldn't be on the front age and/or in a special section of the site (which it wasn't anyway) and it still got whistled.
Does anyone else believe that people are abusing their whistles when it comes to reading reviews?