The Cubs have always been the biggest draw for the valley in spring training.  Their contract with the city has run out.  They were threatening to move to Florida but a deal has been worked out which includes a new $84 million dollar training facility.

http://www.azcentral.com/community/mesa/articles/2010/01/27/20100127cubs-keep-spring-training-in-mesa27-ON.html

And this is why the Cactus league is so much better than the Grapefruit league for watching spring training:

When the Arizona Diamondbacks and the Colorado Rockies move from Tucson to a new stadium on the Salt River-Pima Maricopa Indian Community next year, all 15 Cactus League will be no more than an hour's drive from each other.

In Florida, teams are scattered throughout the state, with stadiums hours away from each other

So how many of you come out in March for this?

-- Modified on 1/27/2010 11:08:58 AM

south of I-4 with some on the east coast (Marlins, Cardinals, Mets, Nationals), center of state (Astros, Braves, Tigers), and some on the west coast (Yankees, Phillies, Jays, Pirates, Orioles, Rays, Red Sox, and Twins).  The teams in the center of the state are less than 2 hours drive to either coast.

in other words within a hour's drive at the most of each other.