FFAs are the carnies of the search engine world.
An FFA will keep your link on for a bit and then drop it when it gets "pushed" off the page by other links causing fluxuations in your PageRank and lots of confusion in your brain. Sometimes your links won't last until the update(s).
Some FFA engines are being PR zeroed and others have been dropped altogether because they exist for the sole purpose of fooling the engines into thinking that you're popular when you aren't.
Absolutely zero traffic will come off of them (besides the spider that will vist you twenty thousand times a month) and you will receive more spam e-mail than AOL disks in metal tins.
I have heard of some SEO "experts" strategically submitting to make the updates - but then you have to think of how lousy a long-term plan this is since your rank is only as good as the time you put into submitting them again and again to these worthless engines.
Take time instead to gather quality content, post messages on newsgroups (for your own sake - make sure that they don't read like ads), setup a two-step newsletter subscription link or a Members Area (or both) so that you can create a user-base to e-mail with every update of your site, and of course, submit to all of the other engines that aren't FFAs.
There are plenty of second tier search engines like WISENUT and EUROSEEK that will index you - and those are permanent (for the most part) inbound links in categories related to your site. Some of these guys will even throw you into more than one category if you ask nicely. You can probably find a good 50 legit engines... that's a great start as far as inbound links are concerned.
Remember, don't try to fool anyone when it comes to PageRank or doorways - because when the majors change their ranking algorithms again and start universally blacklisting "booster" sites - it may be yourself (or even worse, your client) that you've fooled.
BTW: Just visited your site - wowie zowie you've got your work cut out for you. Is your ROI worth all the fuss (considering the time and money it takes to maintain a site that's been "cookie cut" into infamy)? You're dealing with an industry that is probably second to only the adult industry when it comes to cutthroat tomfoolery.
If you can make it work for you, then more power to you, but definitely do some market research before you jump head first into positioning a site that exist in an already flooded market.