What can you say about the adopted selves in Oscar Wilde's The Importance of Being Earnest?

The adopted selves in The Importance of Being Ernest are traditionally thought of as Oscar Wilde's commentary on the pretensions of Victorian society. Victorian society was highly moralistic and very structured. Every person had their role and were expected--even assumed--to not deviate from it. People married and had children, never stepping out on their spouses and not, under any circumstances, engaging in "immoral" behavior. Wilde himself was a living example of how untrue this was. He was married but carried on affairs with men, eventually initiating an arrest, imprisonment, and trial for "gross indecency" with men. He was an accepted member of high society and a socialite as well as a Protestant with Catholic leanings. He was a study of duality himself. 

The Importance of Being Ernest mocks Victorian expectations that everyone was what they seemed to be. In the play, almost no one is what they seem--or even necessarily what they think they are. Jack poses as Earnest when he goes to the city so he can do what he pleases on the pretense that he is helping keep his little brother Ernest in line; in reality, he "becomes" Ernest and goes partying. Algernon, who poses as the made-up cousin Ernest of Jack to woo Cecily, turns out to, in fact, be named Ernest. Algernon normally uses a made-up friend Bunbury as an excuse to leave the city and visit the country to do what he pleases. When they slip into their alternate realities, the lies become their realities. Wilde knows from experience that this is a reality of Victorian society; he's merely exposing it--confusingly yet comically. Such behavior and illusions would be necessary for many, if not most, Victorians to maintain sanity in such a restrictive society. 

Another way of looking at the question is that Wilde was commenting (perhaps) on the fact that art imitates life and vice versa. Reality, in this play, follows imagination. Take, for example, the fact that each of the friends decide to have themselves christened "Ernest"--Jack, in love with Gwendolyn, who thinks his name is Ernest, solves the problem by deciding to have his name changed; and Algernon, having conspired to meet Jack's cousin Cecily and already posing as Ernest to meet her--and having learned that she is particularly drawn to the name--decides to have his name changed, as well. We also have the example of Cecily whose fictitious realities, created and written to escape the boredom of her life, are more real to her than her actual life.