There are a lot of people that are really excited about the Apple iPad... I'm one of them. The thing has a general coolness factor off the charts, but what excites me most is specifically the way it (and products of it's kind) will affect art.
First, as you know, I have a passion for digital visual art (especially when it exists online). The iPad makes viewing the internet more accessible than ever. To "hold the internet in your hands," as Steve Jobs puts it, in a format large enough appreciate the average website, as opposed to smartphone size, is to become more intimate with cyberspace than we have ever been. People can take the internet with them in public and share it with friends in a more natural way.
As opposed to laptops and desktops, the iPad is truly mobile and that means that, along with the internet, digital art can be carried close to you at all times.
It's touch screen functionality is also more intimate and puts artists and viewers into a more traditional relationship with what is being displayed. I've been using a Wacom tablet for awhile now because it allows me to draw on the computer with a stylus, giving me more freedom of movement and better control than a mouse or track ball. While I'm not sure that the iPad will allow you to work with a stylus, it will definitely allow you to making natural drawing gestures with your fingers directly on the screen. This lends itself to creating a perfect sketchbook out of the iPad and leaves a great opportunity for developers to make drawing apps (finger painting!).
Because it is being offered at a relatively low price point($499 starting vs. $1k for a comparable Wacom tablet), it will be widely available. And the more artists work digitally, the more credibility digital art of any sort will have.
Art created digitally will surely lead to work that makes use of the digital world's unique advantages. Works can be dynamic, interactive, cloned and shared, and viewed instantly all over the world. Artists will find that leaving their work in a digital format (as opposed to printing it out or otherwise bringing it into the physical world) can heighten it's poignancy and sharpen it's effect.
And why should artists have to make the work into a physical object when the iPad could easily double as an electronic picture frame? When it's not being used, people can plug it into a dock and view digital visual art (presuming somebody makes an app for this purpose).
These are just a few reasons why the Apple iPad is making the future of art more exciting.