I am happily married but I have always wondered a couple of things about online dating sites.
1. Are most online dating site setup for male female relationships or are there options for same sex relationships?
2. Do these online dating sites allow the user to search by ethnicity? I assume no but don't know for sure.
I haven't used the online versions. Their predecessors (newpaper personal ads) allowed users to self-identify, and indicate whether they were seeking m/f...but you always had to be mildly skeptical, same as now.
One thing I forgot to mention - the downside of online matchups is location location location. If you're looking for companionship, starting up a relationship with someone 1500 miles away is a bit of a step backwards.