I had LPCXpresso installed and compiling examples in no time. I don't have any hardware to try it out on though.
I bought a LPCXpresso Development Board and installed the software and it was really easy. My problem was that it was only useful for NXP's ARM-based LPC microcontrollers.
I was hoping to drag and drop in Arduino sketches but, some stuff works and some does not.
This is the problem with Maple and with ARM in general. Leaflabs did a great job with Maple but an ARM board can't be really compatible with the Arduino AVR boards.
ARM processors from Atmel, ST, NXP, and other manufactures are not really compatible at the peripheral level. The Cortex-M core helps but you need and OS with a HAL layer to get any compatibility.
It will be interesting to see what the Arduino group does with Due.
I like to play with many types of processors so I will do what I learned to do thirty years ago on huge scientific projects. These projects have a variety of processors in their control systems and data acquisition systems so the they use a general RTOS that supports a wide variety of processors. This allows common software throughout the project. It also allows upgrades of processors over the life of the project.
Most of these projects used commercial RTOSes like VxWorks or LynxOS.
I have been using ChibiOS since it is free and supports a lot of hardware.
x86, ARM7, ARM9, Cortex-M0, Cortex-M3, Cortex-M4, PowerPC e200z, STM8, AVR, MSP430, Coldfire, H8S
I have it running on the Olimexino board. It is really hot, benchmarks at 939,048 task context switches/second. This is for a full switch from one task to another, about one microsecond.
It is much faster at the driver/interrupt level. Here you only need to save and restore minimal context. ChibiOS also has hooks so you can write an optimized ISR independent of the OS for the max possible performance.