The iPad is going to be sweet. It will change the way law students learn the law, and it will be a benefit to practicing attorneys. The iPad will not do anything that another device can already do. It will simply do those things better.
I use my iPhone all the time during client meetings. I can pull up documents using Dropbox. I can access the web to lookup various things: public records, company information, etc. Sometimes we need to make recordings, which is also easily done. I would love to take notes on my iPhone instead of by hand, but it is too annoying.
The iPad can do all of that stuff, and do it better. You can pull up documents on Dropbox and read them without zooming in. You can turn your iPad around and show it to a client. You can access the web and the client can look with you at the same time. You can make recordings. I could also take notes if I wanted.
Could I use a netbook to do all this? Sure, with a smaller screen and a lame interface and operating system. When I need it, my iPhone is a nice sidekick during client meetings and the iPad will be even better.