ABQ, what math games do you like?
I find the ipad's toylike qualities might pose a distraction for in-school use. But if you set a lot of restrictions (don't let the child make purchases, download apps, etc) it could work for some things.
I find that the ipad's built-in word completion cramps my style-- I wish that could be turned off. If you're trying to teach a child to spell independently, that may be a hindrance.
DeeDee
ETA: Dragon for the Mac is also apparently nowhere NEAR as good as Dragon for the PC. Read some reviews before you make that investment.
You can turn off the predictive text and auto editing in the Settings app on your iPad or iPod Touch. Select Keyboard and then toggle on or off for Auto-Capitalization, Correction, Check Spelling. You can also add short cuts - code letters that automatically type out what you want such as omw meaning on my way.
I use the Dragon app on my iPhone a lot to send texts and email while I'm driving, and it gets a few things wrong, but for the most part, it works pretty well.
As to Macbook Air vs. iPad - my college son has a Macbook Air, and, one, it's much more expensive, and two, it doesn't have the tactile advantages that I wanted for my son with dysgraphia. So while the Macbook Air is excellent and can now share DVD or CD drives from other devices (none are built in), it's still a bit like using a Porsche to drive a block to school. That's just my opinion, though. We currently have in our house a Dell laptop, an older Dell tower computer. an iMac, a Mac Mini, three MacBooks, three iPads, four iPod Touches, three iPhones and a Mac Airport - but we also have two companies that develop on the Mac or iOS platform.
One note - if you're planning to get an iPad, the next generation will likely be available in March, and even if you don't get the latest, it will likely mean a drop in price on the iPad 2.
As to games, my son is currently struggling with memorizing times tables and dealing with the visualizations of fractions and decimals, so we're using Hungry Fish, Motion Math Zoom, and Motion Math HD.