Magister's Terrace was the first new 5-man we had since Burning Crusade came out. By then, many of us who'd been around for the beginning of Burning Crusade had run Shadow Labyrinth until we heard Murmur's voice at every waking moment. Sunwell Plateau came long after many 25-man guilds had Illidan on farm, and Death and Taxes even cited the wait for Sunwell Plateau as part of the reason they fell apart. Now, most of us have our 70s up to Exalted with the Shattered Sun Offensive, we've run Magister's Terrace until our eyes bled -- although some of us are dedicated to running it more just because that orb and that bird refuse to drop -- and a sense of ennui has set in. We want more. Patch 2.4.3 is giving us a few new items and a quest, but with at least 3 months to go until WoTLK comes out by most estimates, it's very likely that we'll need more.
It seems to me then, if Blizzard wants to wait 2 years between expansions, that's fine, but they could stand to get a little bit more content out to keep us occupied in those long stretches. Put out a 2.4, with a new 5-man and 25-man dungeon, every 2 to 3 months or so. That should be long enough for us to get tired of running the 5-man, and long enough for a decent chunk of 25-man guilds to get through the dungeon. You could even add a new arena floor or a new battleground to some of these patches to help out the PvPers.
They don't have to be fancy. They can have 2-3 new bosses each, a decent amount of trash, some side-grade or small upgrade drops, and maybe a new pet or vanity item. They can be shoehorned into existing lore or factions. You can give us a new Burning Legion dungeon hidden somewhere in Hellfire Peninsula. You can give us a Grimtotem dungeon somewhere in Feralas or Thousand Needles. If you want to get really ambitious in a patch, you can let us into a really lore-rich area like Uldum or modern day Hyjal.
More consistent new content for all types of end game play: It's an idea whose time has come. If Blizzard can plug up some of these long content droughts with a steady stream of new content for us to explore, it'd go a long way towards customer retention, and cementing their position on the top of the MMORPG heap.