I'm here in New York with the Arduino team (for the Open Hardware Summit and Maker Faire NYC), and the team has just announced the long awaited 1.0 version ("Punto Uno") of the Arduino platform. This is actually just the start of a series of hardware and software evolutions that will take Arduino into even more markets, both broader and higher-end. The Arduino phenomena, as big as it already is, is only going to accelerate from here.
The two main hardware differences in the new board are that the venerable FTDI chip that's used as a USB interface has been replaced with and Atmel ATmega8U2 and the Mega's Atmega 1280 has been replaced by a Atmega 2560, with more memory. Here's how the team describes this:
--"We replaced the aging FTDI chipset with a custom made usb-serial converter built with an Atmel ATmega8U2 this provides lower latency and doesn’t require to install any drivers on mac and linux (on windows all you need is a simple .inf file) more advanced users will be able to reprogram the USB chip to make the board show up as a variety of USB devices (Keyboards, Mice, Joysticks, MIDI etc)"
--"An upgrade for the Arduino Mega which will sport the new Atmel USB chip plus an ATMega2560 processor with twice as much flash memory. We’ve been able to obtain some significant savings due improvements in the production process and better pricing from suppliers that we are happy to pass on to customers. This board will have the same graphic design as the UNO.At the moment, due to limitations in the GCC compiler only 128k of flash are immediately useable but we’re very close to unlocking the whole memory space."
We in the ArduPilot/Copter project, along with Sparkfun, have been working with the Arduino team closely on these changes, and will be making similar changes to the APM board and IMU shield. It's all backwards compatible, so there should be no code issues or differences in performance with the existing boards, but the new boards with the ATMega8U2 should be a bit cheaper to manufacture, and won't require the FTDI driver, which should make things easier for newcomers.