The iPad can be one of the most frustrating devices to write with. It also has the potential to be one of the best, under certain circumstances. I've had the device for a few months, and in this time, it has been used primarily to consume media. It's quite easy to load TV and movies from my MacBook, and there are a number of addictive games, such as Plants vs. Zombies, and Angry Birds available. The web browsing experience is a little lacking. Pages take longer to load than expected, and the cache is small. Switching tabs in the mobile browser often results in a fresh request to the server, adding extra delays. I've found that on some websites, scrolling just doesn't work.
As the iPad doesn't support flash, many of the richer web experiences, as well as numerous flash games, don't work. While I can certainly appreciate the processing requirements of flash -- I often disable flash on the desktop -- the fact remains that there is a great deal of content, including puzzle games, only available in flash.
The on-screen virtual keyboard is functional, though awkward to use. I believe that there is a special place in hell reserved for those brilliant engineers who inflicted the iPad with the horrendous auto-replace functionality. Without tactile feedback, one is forced to watch where your fingers are typing. Because I'm watching my fingers, I'm often not watching the little popup dialog elsewhere on the screen, warning me that the system is going to replace the awesome word I just typed with nonsense. Maybe it actually corrects far more than it wrecks, but the experience can be frustrating.
Still, the keyboard is functional, especially for short notes and emails. Where it is entirely unsuitable is for longer writing sessions, or for speed. Forget about using the virtual keyboard for in depth course notes. Try and type as little as possible in these situations. You're lucky if you can get down meaningful point form notes.
Until the iOS 4.2 update, I had been able to connect a USB keyboard to the iPad using the camera connection kit. While the system claimed that the device was unsupported, it still performed admirably. With iOS 4.2 however, the hardware handling has changed, and the iPad no longer recognizes USB keyboards. I suspect Apple has adjusted the USB voltage, or something else of that sort.
As such, I purchased an Apple Wireless Keyboard, which uses bluetooth. Thankfully, this keyboard is much smaller than the older USB keyboard I had been using, and better still, the bluetooth functionality allows me to charge the iPad while typing. Pairing the keyboard with the iPad is simple, and the keyboard is only slightly wider than the iPad itself. With the keyboard, my typing speed should be about the same speed as on a desktop system. Also with the keyboard is the quick ability to cancel an autocorrect suggestion by using the escape key. As such, it becomes much easier to allow the autocorrect to fix words you misspell, while avoiding any undesired changes.
One clear advantage the iPad provides when writing, is the single-task nature of the iPad. As the iPad only presents a single window, it enforces a single-track mentality. There are no bouncing dock icons, no web browser or twitter to distract you. Just you and your text editor, unfiltered. Much better for concentrating on writing.