At first a bit of a utilitarian mystery, the iPad has evolved, for me, into a practical device.
3G and weight: these, I have come to realize, are two of its best features. Thanks to 3G and its gossamery 1.5-pound portability, I can whip it out anywhere and work, navigate with the GPS, or just relax. And I am doing this with increasing regularity sans laptop.
Always on, always connected: The fact that it's always on, always connected--like a smartphone--makes it the device of choice to grab when moving from room to room inside the house: for watching movies, reading, shopping online, or using it as a phone via Skype. (And another reason why it's great on the road, too.)
Battery life: Typically, the iPad lasts on one charge for more than one day, often two days (sometimes three) with regular use. That is amazing. My MacBook Air lasts little more than an afternoon. That alone makes the iPad more practical than a laptop, at times, when I'm on the road.
All of the above also poses an interesting philosophical question about the merits of traditional laptops versus tablets/slates. But I'll leave that discussion for another day.