If you've read the reviews to date you probably know the basics: The new iPad is a bit faster than the iPad 2, it has more cache, but it also needs that cache to support the high-density "retina" display. If you choose to get the 4G model (I chose Wifi), there are reports of impressive data bandwidth - 14MB/sec or better in some urban areas. Used judiciously, this could be a very good thing. Use that bandwidth gratuitously and you'll go through your monthly data limit in no time, not to mention your battery.
The new iPad is a bit thicker and heavier than the iPad 2, but to tell the truth I couldn't really notice any difference. If you have a magnetic Smart Cover, it will work just fine with the new iPad. Rear cases for the iPad 2 are incompatible with the new iPad and third-party suppliers are only now beginning to get some offerings out there. On eBay I found an inexpensive, bare-bones transparent case for the new iPad that works with the Smart Cover for a mere $12.99, including shipping. Other third-party cases may be sexier, but they can set you back as much as $60, or more.
Early benchmarks seem to indicate the iPad 2 and the new iPad are essentially the same when it comes to processor and memory performance. I find the new iPad a bit faster when it comes to downloading chart updates and the crispness of the retina display is a noticeable improvement when viewing PDFs and Jeppesen's rendered charts. Try something like scrolling through Google Earth and you'll see a marked difference. In general, most any text that is rendered on the new iPad's retina display looks a lot better.
Storage, WiFi, 4G ...
I previously recommended the 16GB iPad as being sufficient for most pilots. Lately I've had to clean out unused apps and data from my iPad 2 because I was down to 1.8GB of free storage. For the new iPad, I chose 32GB and that seems to be adequate for my needs. Then again I have loaded three EFB apps as well as numerous presentations, spreadsheets, and PFD documents. If you want to store a lot of music or a movies for that long airline flight, you may want to give some thought to more storage or consider an external storage device.
My choice was to continue to with the WiFi model rather than go 4G, mainly for budgetary reasons. Yesterday I flew with a pilot who had just gotten the 4G version. Just before engine start, he realized he hadn't transferred his ForeFlight Checklists. No problem. He was able to sync his check list to his iPad over 4G in what seemed like about 10 seconds. As an aside, ForeFlight Checklist Pro, having been designed for the iPhone and needing to be run in 2X mode, looks fantastic on the new iPad retina display.
The downside of 4G would seem to be battery life. After a 1.5 hour flight, the battery on the new iPad 4G was down to 5% from almost being about half charged at the start of the flight. More investigation needs to be done, but it would appear that disabling 4G or using an auxiliary power source in flight is a must with the new iPad. After two solid days of flying, my new iPad WiFi battery life seems exactly the same as the iPad 2.
Another preliminary observation is that my new iPad may run a bit warmer. Right now the weather is cool in Northern California, so time will tell if the extra graphics and cache will contribute to higher operating temperatures. Right now, I haven't seen any heat-related issues.
Upgrade or Wait?
To buy or not to buy? That is the question for many pilots. If you are an original iPad owner, moving up to the new iPad is a no-brainer. If you currently own an iPad 2, I don't see a pressing reason to upgrade unless you need 4G performance, you have filled up your storage, you have need for the retina display, or you just must have the latest/greatest and you have the requisite disposable income. If you do choose to trade up from the iPad 2, you'll undoubtedly be able to sell it for a higher price now than if you wait until the next product offering.
Rumors abound about a smaller form factor (7.85") iPad being released in October 2012 to compete with the Kindle-sized readers. A smaller iPad could be a viable device for yoke mounting in an aircraft, but we all know about rumors. The reasonable assumption would seem to be that any follow-on to the new iPad (whatever it will be called) won't hit the market for at least another year. The bottom-line for me is that the new iPad WiFi is drop-in replacement for the iPad 2 and performs just a well as its predecessor.