Remember when the beta for The Burning Crusade beta went live? It didn't take that long until it was released. When do you think Wrath of the Lich King will be released?
One guess we can make is that it will be after Blizzcon, so at the earliest sometime in October. However, it's doubtful that it'll be released the same month as said event, my guess would be November or around the Christmas rush in December. Being even more realistic, I'd say January, so they get plenty of testing, tuning and polishing in—it's blizzard we're talking about afterall, folks.
I can't help but to speculate and discuss this topic with people though. Wrath of the Lich King seem to be introducing a lot of content, about the same amount as in The Burning Crusade. Hopefully it will have the same quality and polish as we've come to love about Blizzard's titles. Knowing that they're actively developing Diablo III, Starcraft II and another top-secret MMO alongside of the Lich King expansion is both positive and negative. However, if anyone can pull it off, I'd say it's Blizzard.
The fact that they have told us how they want Arthas to be more involved throughout Northrend than how Illidan was in Burning Crusade only makes it even more appealing than TBC. Furthermore the Achievement System was just announced and it's going to be yet another reason for players to keep their accounts active.
You can easily tell that Winterspring is one of the favorite zones in the game too. Having a icy and snowy continent is awesome, since players have wanted to experience more "cold" enviorments for awhile now. Plus, going back in time to the famous MMO EverQuest – it has an expansion called Scars of Velious, which is an icy and snow continent. Said expansion remains as one of the (if not THE) best expansions to EQ up until this day.. and they now have something around 14 expansions or more.
Now, taking all this into account and attempting to be logical—will they aim for more money (Christmas rush) or simply take their time and ignore peer pressure from Vivendi? I'd say ignore the pressure, since they can release this title whenever they want to and still sell like crazy. To many the new expansion feels more fantasy-like compared to Burning Crusade and Lich King is also more grim and dark, which it should be.