WoW is over 6 years old. Newer, flasher games come out, are deemed "WoW clones," but still manage to keep a portion of their playerbase just because some folks are tired of WoW itself. How many times do people reroll, regrind, re-earn achievements on alts, etc, before burning out? While community certainly helps with retention, I'm sure a lot of us have some special activity that keeps us going.
On Dragonmaw, we have something called Friday Night Fights. A multi-guild, cross-faction group hosts usually one open server event per month, but the rest of the time, it's limited to only certain guilds, to keep the sides fair (at least at the start, till others see what we're doing and join in, hehe). Each week has us fighting in a different zone, usually over an interesting feature in the zone. We've fought on the Deepholme airship, on the Thandol Span that links Wetlands to Arathi Highlands, even got folks doing Halaa again.
Recently, we tried something totally different: nub races based on guild names. For example, members of The Earthbound ended their names with "bound," so "Leeroy" came to the event as "Leeroybound". First nub to die on the designated faction leader as their guild-nub got bragging rights for their guild, and the other participating guilds had to lavish praise on the winners. Cries of "Tigers!" and "Not the murlocs!" were heard all night, and guildies who didn't have time for the whole race popped in just to watch/kill the nubs during their epic adventure.
I burn through patches quickly, especially dungeons, but I always look forward to Friday Night Fights. Do you have some sort of special playstyle or event that you use to keep WoW feeling fresh?