Arduino Due - What should I know about it?

Ok I bought an Arduino Due, I should have it in a couple days.

I would like to hear from people who are using them. This like differences in code, compatibility with shields and stuff like that.

and is the 3 volt limit only for input into the board?

Did your read the info on the Arduino.cc site ?

The reference of the board : https://www.arduino.cc/en/Main/arduinoBoardDue

A guide how to use it : https://www.arduino.cc/en/Guide/ArduinoDue

You start with the Blink led example. On the board is a led "L", which is driven by pin 13. Not all shields and libraries are adapted for the Due. The Arduino shields with version 'R3' are compatible. For example the Ethernet Shield version 'R3'.

Sensors to the I2C bus are often compatible of course, since the Wire library (Wire library is for I2C) has the same functions for all Arduino boards.

I have been using the mega and uno for a while, was just curious about common issues people have run into and specific differences in code

Well, the ARM core is totally different from the AVR Arduinos so things that worked on Uno and Mega won't work on the Due. Writing a sketch for the Due is a good exercise in ONLY using the standard Arduino functions and not using unportable tricks like direct port access.

The datasheet for the chip lists lots of cool features like RTC, Ethernet and DAC but they are either somewhat limited (DAC) or totally unusuable on the Due board (Ethernet). Even the 12-bit ADC is badly hampered by the board layout. Lack of EEPROM is a problem for many people too.

I've yet to see an Arduino sketch which actually needs 32-bit integers or the extra speed of the Due. There must be sketches out there which usefully use those features but they're not being published or advertised here. The main usefulness seems to be simply the extra program space.

The 3v limit is usually not a problem. Many sensors are 3.3v and anything that is 5v can understand 3.3v logic levels and a voltage divider fixes inputs to the Due.