MacLife has a good rundown of the differences between the iPad 2 and the new iPad that was introduced this week (not called iPad 3). Their bottom line?
The iPad 2 remains a really great tablet. If you don’t plan on using the cellular network, sticking instead to Wi-Fi, the iPad 3’s 4G capabilities are wasted on you. If you don’t care about shooting photos or videos with your iPad 3, its fancier camera is wasted on you. That leaves you with a better processor and a very beautiful high-res screen — for some this will be worth the upgrade, but for many, it won’t.
My main reason for wanting to upgrade from my first generation iPad to the newest version is primarily about storage. I have the same problem that the author of the article above has: with 16GB I often find myself swapping in and out apps, videos, photos, and other files, since not everything will fit at the same time. The new iPads are available with 32 or even 64GB of storage, but you can only find the iPad 2 in the 16GB size. If you’re fairly sure storage won’t be an issue for you (and for many it won’t be), you would likely be served well by an iPad 2 and an extra $100 in your pocket.