lately i dont watermark my members area movies for a variety of reasons, mainly because i dont like to compile 2 versions of the same movie (1 for web and 1 for dvd) which takes forever.
if people are gonna rip off your content theres not much you can do about it except DCMA them when you find them, but you can "brand" yourself by repeatedly mentioning your website and your happy members throughout your videos. realize this works, as many people join amateur sites not for the videos alone but for the 1-on-1 interaction they get from the site owner/models/etc. they may can steal a 20 minute video but they cant get the full story behind the scene, interact with other paying members, etc if they are on the outside. i only watermark my free "crap content" that i feed to the tube sites. usually the stuff that doesnt make the final cut, bloopers, etc. free users get the dregs, paying members get the champagne