The Army uses Apple  products for a host of reasons. They're durable, easy to use in the field, tough to hack, and readily available (unlike many specialized computer hardware items). They've been known to use iPods Touch as simple translation tools  (they can translate and say "get down!" in Arabic--useful in our worldwide exportation of freedom!). So what went on in Cupertino?
From the military's site:
Apple officials gave the Army group tours of its laboratories and other facilities and talked about some examples of where the military is already using Apple technology. The Army's research and development command is evaluating commercial hand-held solutions such as iPad, iPhone, iPod, iMac, and MacBook platforms.
It's not made clear exactly what the Army plans to do with the iPad--but its large screen, faster processor and ability to display a large amount of text would make it an excellent digital clipboard. It'd be an easy way to deliver new briefings and other information to the troops (or as they dramatically call them, "warfighters"), if they can work out security properly.
But the Army is looking seriously at cellular technologies for transmitting and receiving information in the field--I'm not sure how that'd work in places without cellular service, but it's clear that they'll be working with Apple to equip our fine fighting men and women with the prettiest gadgetry out there.