I joined aebn.com; and also Hotmovies.com and Adultdvdempire.com vod.
Aebn.com definitely has the edge imho. Mainly because playback in pay-per-minute format works best (for me) using Realplayer. AEBN has this facility while the other two do not. Skipping through a film to different parts is much more user-friendly with Realplayer.
The pay-per-minute thing has been really useful for me in previewing movies before making a purchase. With the result that my purchases of late have been much less 'blind' (and sometimes disappointing) in nature.
The flip side of the coin is that you consequently lose the 'surprise' (excitement) factor of seeing something which you haven't seen before when your film arrives.
This type of service is also convenient (no need to dig your discs out) and opens up a whole new world of porn which you might not ever otherwise have access to.
[Link]