The IDE comes with the possibility to display a schematic (as a PNG image) for every project so the user can have a better general "picture" about the project. And I like the IDE colors much more than those of the Arduino IDE.
Another important feature is a better support for 40 pin Atmel microcontrollers. Too bad the Wiring project is not updated more frequently - all Arduino enthusiasts must know the roots of Arduino project by trying Wiring. Just telling a story about Arduino's history is not enough (or fair).
I had hopes that the promise they made on the first page will be honoured, but it seems that they are short on man power (it is a pity that this great project lives in obscurity):
"The current AVR8 Core supports the Wiring hardware and any hardware based on the AVR atmega processors. AVR Xmega, AVR Tiny, TI MSP430, Microchip PIC24/32 Series and STM M3 ARM Cores will be available soon."