The iPad seems targeted at people who want to "consume" content and aren't really looking to "create" content. Meaning, if you want to check your email, surf the web, watch video, listen to audio, play games, read a book, etc. then this device will do it all without the fuss of having to carry around a laptop.
If you need to, say, write a paper or put together a presentation or edit a movie... basically any sort of "creating"... then you still need a laptop or desktop.
The iPad seems like a great tool that could be use as supplementary computers in a household. If you've got one primary computer that is shared amongst a family of four, buying an iPad might make sense.