No high-speed internet. Ever been to a conference where they gave you a drop cable and you plugged it into your Gigabyte Ethernet connection and were uploading YouTube videos faster than you could fill in the title? If so, be aware that you can’t do it on the iPad because there’s no ethernet connection. Correct me if I’m wrong but I don’t think there’s a docking or dongle solution for that either.
Videoconferencing. Another major roadblock for anyone that uses Skype video or similar. There’s no webcam and no ability to plug in a USB cam.
Browser not 100% compatible. The Safari browser is good but it’s not a desktop browsers and therefore you will find issues. If you have critical web-based productivity tools, make sure you test them before buying an iPad.
Programming and coding. Not on the iPad.
Limited storage. For $499 you get 16GB of storage. (14GB available I understand) I can blow that in a single conference with images and video. Be careful if you need to store big docs, images, videos or CD/DVD images.
Use DVD/CD/BluRay media Speaking of CD/DVD, you won’t be able to plug in an external drive to play videos, presentations or to run learning tools from a CDROM.
Expand memory/storage As time goes on, the specifications on your device get less and less impressive. Memory requirements go up, connectivity requirements change, storage requirements go up. The iPad is a sealed unit and there’s no upgrade path.
Run pro-quality apps. (Music, graphics, CAD, dev environments, office suites) This is fairly self explanatory although as time goes on, this hole will gradually be filled by the app store. However, I don’t see high-end pro-level apps ever being ported to the iPad based on effort required and low pricing points in the app store.
VGA/Digital video output (presentations, desktop monitor) With a dongle you can get 1024×768 VGA output which is enough for presentations but there’s no digital video output and nothing that allows you to work with higher resolutions.
Charge a phone (from the USB) I do this all the time. In fact I charge multiple devices from my UMPC. See image right.
So, there’s a nice big list of things to think about. I’m sure you’ve got thoughts, both positive and negative and as I’m not an iPad owner (yes, I know. If you’re an iPad owner it’s difficult to take this from someone that hasn’t even touched an iPad yet) I’m happy for owners to correct me or offer solutions.
As for alternatives that might be more useful in a productivity scenario, here’s a few to take a look at. All of them have their own issues but there might be one there that fits you better than the iPad.