Past Ren guests were invited to sign up to be charter members of Oceania's Club. I believe that the deadline for that has expired. However, don't fret, I don't believe it's done anything. Maybe it will in the future. I think it will "entitle" you to promotions on "select sailings".....no biggie.
For a real benefit, you should join the Oceania Cruise Group on Yahoo. You'll get to meet cruisers going on your sailing and can exchange port and excursion information.
We prefer independent travel and hooked up with another few couples to create our own "tour groups" of 4 or 6 and then exchanged a lot of information online.
Additionally, if at least 20 people sign up, Oceania will throw you all a cocktail party. We had about 60 people at ours.
It was so much fun going onboard and having so many friends to hang out with!