re: multi-tasking, technically, it can, it's just not available to third-party apps.
It is not a laptop replacement, nor is it intended to be, it's something different. As someone else alluded to, and several reviewers have also mentioned, it's not targeted to the tech crowd per se, it's for people who want to not play with or upgrade their computers, they want to read mail, browse the web, play some games, look at some videos, and listen to music.
Another thing it does is open up other possibilities because of its form factor. This will become the device of choice in hospitals and other data-consuming activities. My manager, who is not an Apple person, wants one now to keep his flight charts in, rather than lugging around a big book or some of the specialized devices for this.
It is not revolutionary in a technical sense - what it does, and what Apple excels at, is combining the features that the majority of people want, and making them behave in an intuitive, cohesive fashion.
I haven't bought one, and am unlikely to do so. My laptop serves as my computer, and my iPhone serves as my general on-the-fly browsing, mail, and phone device. When they get another generation or two forward, and my laptop gets long in the tooth, I'll look really hard at one. If she didn't already have a late-generation iMac, one of these would be perfect for my mom (the one caveat being that at present, there doesn't appear to be a way to print from the thing).