I use it daily for business and it has been a great tool that allows me to do everything I need. I use the basics from email to web, but the Goodreader app let's me carry blueprints and PDFs with me that I never bothered carrying before. I use RDP and VPN functions to the companies order entry system and RDP to my home computer when I need a document to be dropped into Dropbox or iDisk.
I take my iPad everywhere, it's how portable computing should be imo. I don't need a 5 lb computer with 3 hours of battery life to read documents, show plans and do what I need. Any major project or bid is created when I'm in the office and on a workstation, the iPad has sold product for me simply because it was in my hand and ready when I needed it. I carry it in a portfolio vs a laptop in a bag with a charger and all the crap I used to never bother taking out of my car. Now I always have the resource whenever an opportunity arises.
List of apps would be:
Good reader
iAnnotate
Dropbox/iDisk
Evernote
iWork suite of apps as well
The funny thing about the iPad is the conversations it leads to. I've sat with a client that usually is all business, if you schedule a 30 min meeting you better be done and and be out of his office. Sometime this past August I dropped in just to say hello, no appointment, just a quick in and out. He was on the phone and I could hear him talking about looking for some warranty info on a product my competition sold. I loaded up the info on my iPad, and when he came to say hi I showed him the PDF from the site and already emailed it to him. Clearly happy that I had done this for him he invited me to lunch, a rarity, and we proceeded to talk about anything but business for nearly two hours. I was in shock, as he was impossible to corner for meeting let alone lunch. I learned more about his personal life and his interest in gadgets that I would have not likely have learned otherwise. Talk about an icebreaker.
This is not the only time the iPad was a great icebreaker for some of my clients that were interested in it and how I used it for work. Sure it could be any tablet but right now the iPad is what I own and love for my daily needs.