Direbrew and the Mounts
The inaugural version of Brewfest in 2007 had a relatively straightforward focus; ride the frustratingly lag-prone ram race into the ground, and get your own version of the mount as a souvenir. In '08, the mount (and its promised Horde-model counterpart) had been pulled from the vendors to serve as an incentive to get players find a group and travel halfway around the world to kill a boss who frankly wasn't that challenging even then. Direbrew dinged to level 80 in Wrath, but there was so much raid gear inflation by the time October 2009 rolled around that his updated stats were already trivial.
Today the automated dungeon finder finds a group and teleports you directly to the boss, removing the two previously time consuming portions of the event. With even more raid gear, the fight runs so quickly that you probably won't be in the instance for more than 60 seconds counting time to buff, pull, and loot, even if your tank is some kind of incompetent noob (sorry PUG's, three Brew-fails was enough).
As Larisa notes, the event is now so quick and easy that Blizzard might as well mail out the rewards to everyone once a day, for all the effort that it takes to click "join queue" and "enter dungeon" (generally 1-5 minutes later, actually doing DPS is somewhat optional since the fight will be over before anyone notices).
The Achievement Circuit
In place of the mounts, the ram race tickets now award items that are used in the infamous holiday achievement system. This too has been nerfed into the ground.
Brewfest '08 happened before achievements were added to WoW, but those of us who were paying attention could see the planned requirements in the beta. The Brewfest achievements which were listed in the achievement window when Wrath of the Lich King went live in December 2008 required that players obtain the rare mount, spend 550 Brew tokens on other items, and log in at least once a month for a year to collect and drink the beers from the "Brew of the Month" club.
Blizzard had intended the coveted 310% mount reward to be as rare as its raid and PVP counterparts. Unfortunately, the system did not do an adequate job of warning players that they were in for a difficult grind that most were intended to fail due to the vagaries of the random number generator. Players (myself included) did not appreciate learning this lesson AFTER investing hours on frustrating event grinds, and Blizzard was forced to respond by nerfing everything.
By the time October 2009 rolled around, the mount had become optional and players were only required to join the Brew club, not actually stick around for a year to consume the beers. This year's version nerfs the event even further, removing 350 tokens from the required count by making the festival outfit optional. I'm not sure if this change was made because 550 tokens requires a lot of frustrating ram racing for a single year, or because Blizzard and/or the ESRB does not want to force players to consume in-game alcohol - another achievement for getting drunk and falling the maximum non-fatal distance was also removed this year.
Either way, I had the Brewmaster title on my Tauren by the third day of the two and a half week event.
Whither Brew Future?
I've long criticized Blizzard for turning its world events into time-sensitive grinds, as if the amount of time players spend on an event is more important than the amount of fun they have while doing it. Perhaps the newly lowered Brewfest bar is a step in the right direction, or at least an experiment to see how many players will continue to do more involved achievements (such as collecting the outfit) even when they are not required for larger meta-achievement rewards.
The situation with Coren Direbrew is a bit more difficult. Though the new model is a bit too easy, finding a group and hoping that they weren't out to scam you out of your daily summons (each character was allowed to summon the boss once per day) was not an ideal way to set up something that the player is intended to do each and every day while the event is live. The actual fight was equally easy, so the only "skill" the old model required was the patience to find a group each day.
My suggestion would be to move the random chance to get the mount to a non-repeatable (once/festival/year) quest to track down Direbrew the old fashioned way, without the help of the dungeon finder. This would leave finding the mount purely to chance (the drop rate would be improved to take the single chance per year into account), but that is already the case today. The time investment to find a group and travel to the dungeon would be more reasonable as something that players only need to accomplish once in a relatively lengthy holiday.
Like most of WoW, Brewfest this year is in a bit of a holding pattern as everyone awaits the new expansion. I just hope that Blizzard comes up with something a bit less trivial for next year, once the dust has settled on the Cataclysm.