I joined a high-end raiding guild a few weeks ago in World of Warcraft... and it might seem counterintuitive, but I've actually wound up playing less because of that. Heh, my dad would be caught between glee and suspicion on reading that sentence, but there it is. For one thing, I think I'm done grinding for reputation with the factions that need it, and I'm bad at some types of farming and uninterested in the rest. But more importantly, now that I have the option of raids on MC or ZG or Ony, I couldn't care less* about 5-man instances or battlegrounds. Whining idiots yelling at each other to play even more defensively for a few hours? A ninth attempt at a 45-minute Baron run? A UBRS run falling apart after killing the Beast when the tank gets disconnected? Pshhh.
But the raids require a several-hour chunk of time, relatively uninterrupted, unlike that other stuff. So after the third or fourth time I got invited by the rogue leader to join a raid, only to tell them that I would only be on for a few minutes, I began logging on for a few minutes less often. These days I log on for at least three hours or not at all... and I have five pieces of Nightslayer to show for it. :-)
* I couldn't care less on my rogue, at least, my oldest character who had done almost everything there was to do except for the end-game raids. My other level 60 character, a druid, still has quite a few 5-man instances in his future.