From Arduino's Blog:
The new Arduino 1.5 software brings a number of improvements, some in support of the new Arduino Due board and others to make it easier to install libraries and to simplify the boards menu. While these new features should work well, we expect to get lots of feedback and to iterate on them in future releases of the Arduino software.
That also applies to the new (experimental) libraries for the Due, which add features like USB Host, audio playback, and cooperative scheduling.
In the short-term, if you’re not using the Due, you might want to stick with the current 1.0.x (AVR-only) releases of the Arduino software; Arduino 1.0.2 will be out shortly. In the long-term, though, we’re going to be basing the Arduino software on the Arduino 1.5 code. Here’s an overview of the improvements and changes... Read more