In a pair of pieces on the main site today, Wizards announced that they’re changing how they handle the core set. You can read the piece-by-piece breakdown here and Aaron Forsythe’s article about it here. Here are the big changes:

• The sets will now be named by year – for example, the next core set will be “2010,” rather than “11th Edition.”
• Starting with the 2010 set, which releases this year, core sets will release annually each July, rather than bi-annually.
• About half of the cards in the set will be new.
• Core sets will be legal until October of the year following their release, meaning they’ll be legal for about 15 months (and there will be 3-month overlaps between core sets).

Aaron explains the reasoning well in his article, and I agree with him across the board. Let’s quote him a bit here:
Our core sets are typically the best way to teach and show off the world of Magic: The Gathering to the uninitiated, and to that end I believe they need to be as resonant and flavorful as they can be first and foremost. The core set should play into most people’s preconceived notions of fantastic creatures and spells, and those notions should guide them to understand the goals and mechanics of the game.
In the beginning, Magic relied heavily on this kind of flavor. Rock Hydra, Vesuvan Doppelganger, and Fireball are all considered complicated cards from a pure rules standpoint, yet each of those was beloved by players just getting into the game because of how they “felt.” Most fantasy fans have had experiences of one sort or another involving a hydra, a shapeshifter, or a fireball, and to see those concepts spring to life in a card game where they were in command