With all due respect, I don't see how G-Man, Cash, Big-O style video clip posting would be considered "fair use". To begin with, "Fair Use" is a legal defense, not a right. If MGM sees that you're posting clips of their movies - especially clips where characters are killed (spoilers) they can sue you - simple as that. NOW you have the option to use the defense of "Fair Use" in court while you're spending thousands on legal fees... just NOT my idea of fun!
Personally I see the whole "movie review" defense as assuming a judge with an IQ in the lower double digits. In fact if you bring this up as your defense he may be offended that you would even attempt it and tell you to stop insulting his intelligence. The site is set up as a paysite. People pay to see the clips - all the ads for the site display the clips as the reason to purchase membership. I can just imagine a lawyer from Paramount or Universal being completely flustered by this defense... No, I see them laughing at it! And I see a Judge completely sympathetic to someone selling Hollywood clips for the purpose of Death Fetish masturbation... No, if you're lucky you WON'T get a religious Judge looking to give everything you have to the studio and putting you in jail.
Common myths and misconceptions on Fair Use:
http://www.templetons.com/brad/copymyths.html
http://w2.eff.org/IP/eff_fair_use_faq.php
http://www.copylaw.com/new_articles/copy_myths.html
http://www.llrx.com/features/bloggersbeware.htm
Example:
3. Since I'm only using a small portion of the original work, I don't need permission.
While "fair use" can't be defined with mathematical precision, courts have consistently held that "you cannot escape liability by showing how much of [a] work you did not take." Based on the particular facts of a given case, courts will weight the following factors to determine whether a particular use is a fair use: (i) the purpose of the use, including whether the use is primarily for commercial or noncommercial purposes; (ii) the nature of the work; (iii) the amount and importance of the portions used in relation to the whole of the original work; and (iv) the effect of the use on the potential market, or value of the original. Accordingly, even if what you copy is quantitatively small, it may be qualitatively important, and therefore an infringing use.
Sorry for the harsh tone - I wish you all the best and don't want to see you in trouble.