Anyone interested running Arduino (generic) code, or using Arduino libraries (like Adafruit) on LPC13xx (or almost any other LPC), check this out: Arduino-XC - LPC1347
Very usable (UART, SPI, I2C, half a dozen of Adafruit libraries: ADXL345, BMP085, GFX/LCD, ST7735, TCS34725, LSM303) but still under heavy development.
Here is a short video of LPCXpresso 1347 board running code from Arduino IDE.
Compiler and uploader are from LPCXpresso IDE installed on the same workstation. This is proof of concept which uses libraries that come with Arduino-XC (SPI, Serial, Wire, some Adafruit libs etc.).
Serial Monitor seems to have some issues with FTDI USB serial dongle I'm using, so I just used minicom to display serial data coming from the board.