Great second "computer"
My girlfriend is always on my MacBook, while her similarly-aged Windows XP laptop sits there unused*. Quite often we'd both like to be using the Mac at the same time. Getting a second "proper" computer (which has been hinted at) would be expensive and overkill.
The iPad seems like an ideal second "computer". It'll do the majority of what we both use the MacBook for on a daily basis - checking email, reading the web, and even editing the odd document.
Because the iPad is not be a "proper" computer, and is designed to sync with your "main" computer, buying an iPad wouldn't create the annoyance of having to manually maintain and synchronise two separate computers (like a netbook would).
Tempting... and cheaper than buying her a MacBook...! :D
(* Windows XP laptop hated because it's treacle slow and irritatingly cluttered. Hibernate/sleep could be used to avoid the glacial "power-on-to-actually-useable" time, but doesn't seem to work reliably... I guess I need to take a look at it. It was a fresh install only a year ago.)