Image Source: circuitstoday.com
Seeing the diagram, you can easily guess about the customization scopes of Raspberry Pi. It comes with a 700Mhz ARM processor, 256 MB RAM, an audio jack, USB port, Ethernet, RCA Video jack, HDMI port, SD card slot and LED holders. So it is more like an educational board in which you can make lots of interesting applications. You can read a lot about the history of Raspberry Pi – its formation, alpha boards etc on the wiki :- Raspberry Pi Wiki
Jon Orlin has written a great article on how to get started with Raspberry Pi at the beginning -like how to setup the operating system etc. His article is available in techcrunch :- How to get started with Raspberry Pi
Now what do you think are the possibilities of a board like Raspberry Pi ? What all stuffs can you make? Just read the 2 articles below. It will give you an idea of the scope of something like Raspberry Pi or an Arduino.