Academics who have studied the industry believe that it and other forms of electronic communication such as e-mail and social networks are starting to have a significant effect on the ways in which people find love.
In a study presented at the American Sociological Association's annual meeting in August, Michael Rosenfeld of Stanford University and Reuben Thomas of the City College of New York reviewed data from a survey of more than 3,000 Americans with romantic partners.
Outraged critics claim such services deliberately promote infidelity to further their commercial ambitions.
Yet while looking for love online is no longer seen as an act of desperation, the digital-dating industry still generates plenty of controversy.
Few other dating sites have provoked such a public backlash.