https://randoof.wordpress.com/2011/09/05/the-arduino-uno-or-duemilanove-from-one-to-the-other/ , Diferences between Duemilanove and Uno.

The removable ATmega chip also means that when you complete a project and wish to use it, the chip can be removed and used in place alongside either a cheaper cloned version of the Arduino, or even make an Arduino yourself with the correct hardware, which is a lot cheaper than the Arduino and can be a lot smaller as well. For some idea of what can be achieved and for inspiration, have a look at this forum thread.