Whether it's movies, gambling, oil, health supplements, or online dating, the way to judge maturity is the same – when the Feds decide to regulate it in some fashion.
While the shady players or bad business practices may never go away, at some point Uncle Sam decides that Halliburton needs to at least pretend to care about the safety of its pipelines, or that compulsive gamblers probably shouldn't be kneecapped behind the Stardust when they lose big.
Put another way, once you get big enough, taking obvious legal risks for financial gain makes less business sense than providing smooth reliable quarterly results for your investors.
Other than general Internet and ecommerce rulings, we haven't really seen the federal government go after online dating claims/methodologies/terms of service specifically. There has been a fair bit of private litigation against individual sites for discrimination against gays/lesbians, and there is a general lack of "accessibility" for transgender users outside the adult personals… but for now, dating remains basically on an even regulatory playing field with any other type of online business.
Which, to me, says that it has room left to grow.