I'm not a fan of playing a 'mate' with others I don't know, game or not. This especially counts online, because unless you've physically met that person you don't know who's behind the other character. Besides, I'm not a fan of the whole lovey-dovey scene anyways. If it wasn't present, I'd always be nervous that it would in the future. Plus some people take the 'mate' role too seriously, and some other personal issues I have with the 'mate' role in general... No thanks!
Mate Centers are usually fun to watch though, but not because people are searching for a 'mate' there.