Although it should not be difficult to get sketches written for previous Arduino versions working with Arduino 1.0, that release has important changes you need to be aware of. The first thing you will notice when launching the software is the look of the IDE. Some icons are different from previous versions of the software and there are changes and additions in the menus. The error messages when dealing with selecting boards have been improved and the new ADK, Ethernet, and Leonardo boards have been added.
More significant are changes in the underlying core software and libraries. The stated purpose of 1.0 is to introduce disruptive changes that will smooth the way for future enhancements but break some code written for older software. New header files mean that older contributed libraries will need updating. Methods in Ethernet and Wire have been changed and there are subtle differences in the print functionality.
New functionality has been added to Streams (the underlying class
for anything that uses
statements), Ethernet, Wire (I2C), and low-level input/output.
Improvements have been made to the way libraries handle dependencies and to simplify the support for new boards. Because of these changes, third-party libraries will need updating, although many popular ones may already have been updated.
The file extension used for sketches has been changed from .pde to .ino to differentiate Processing files from Arduino and to remove the inconvenience ...