I wouldn't say night and day as I am pretty sociable to begin with, but it really depends on the type of club and the people there. I find if I take a fair bit of MDMA my focus is really on dancing. I would hate to go to a mega-club that just played top 40s with overpriced and watered down drinks when rolling. I would probably leave. Now if it was a proper electronica club like Tresor in Berlin or De School in Amsterdam, then I am a mad man on the dance floor. I really just enjoy dancing, with or without people - more than "socializing" necessarily.
It also depends on the dose. I find a lower dose more sociable and a higher dose less so. For social stuff, less than 80mg of pure MDMA does me nicely. If I am having a mental, dance-my-ass-off kind of night, I could go up to 300mg (but I am fucked and a half and not really able to socialize at those kind of doses, also that's a neurotoxic and ill-advised amount).
My ability to pick up girls and stuff is probably diminished by MDMA over 50mg tbh, but I don't ever take it with that purpose in mind. Overall, I don't think it really changes me too much and people interact with me in basically the same way. Probably more lovey-dovey with my friends and I can't stop dancing.