I would suggest that once you find someone interested in joining you, you correspond by e-mail and then phone a few times just to get a "feel" for how compatable you are. Two rather quiet people might be boring, but even so, it should make it easier for both of you to strike up conversations with other people on the ship since others will be more at ease talking to "two friends" instead of some lonely guy, assuming you are a man, Bob ?? This should work no matter whether you are a co-ed pair or two buddies. That would be the best way to meet some nice ladies since girlfriends travel a lot more together than 2 guys. If you find the other person talks too much, then you better be planning to get away from them and do your own thing a lot.
I've had one male cabinmate, but he was the cruise director of the hosted singles group I went on and he was too busy planning stuff for me to ever get to know him much. He never even answered an e-mail before the crusie. Didn't matter so much there since there were 27 women and only 7 guys in the group and we ate every night together and many times at breakfast. The other time was with a nice lady and we e-mailed a lot and talked about 4 times on the phone before meeting at the ship so we were comfortable with each other and it worked great. We ate almost every meal together.
I will not go cruising alone ! I tell people its boring on the ship after about 2 days unless you have some friends to do stuff with.