So what exactly can I do with one of these? What do I need apart from the Launchpad to get started? Would someone be so kind to explain that to a microcontroller-newb?
If you just want to make an LED flash and play with a couple buttons you don't need anything else--the development board includes everything to hook it up to a computer and program it using Stellaris' software: http://www.ti.com/lsds/ti/microcontroller/arm_stellaris/code...
If you're totally new to electronics and microcontrollers, Make magazine has a good book to check out: http://www.amazon.com/Make-Electronics-Discovery-Charles-Pla...
Better use a real-time scheduler like TNKernel[1] or FreeRTOS[2]. BTW FreeRTOS commercial version is included in ROM on some TI Cortex-M MCU.
The processor on this chip is an ARM cpu with floating point support, probably not something that most would consider exceptional. But for a microcontroller like this, the most interesting aspect is the on-board peripherals. Most MCUs will have some sort of analog to digital converters, counter/timer blocks, etc. You can download the datasheet for the Stellaris chip in question from here: http://www.ti.com/lit/gpn/lm4f120h5qr
Some of the highlights: 12 counter/timer blocks. They each have a capture/compare block which can be used, e.g., to measure timing of external events or output a PWM train (for digital to analog conversion). The timers can also trigger the start of a DMA transfer or the start of an analog conversion.
A 1 million sample per second A to D converter with 12 bit resolution. The ADC has hardware decimation support (up to 64 samples), which can be used to trade off sample rate for sample resolution. The converter also has a 12 channel input multiplexer. Also, unlike the ADC in your sound card, this has DC-coupled input, so there's no lower cut-off frequency.
A DMA controller with support for scatter-gather modes. Transfers can be triggered by the completion of an A/D conversion, the comparators, the timers, or by software.
Two analog comparators: The comparator output can be used internally to trigger interrupts or start a conversion on the ADC.
*There are 8 UARTs, 4 synchronous serial ports, and one each I2C, CAN, and USB controller. So you can talk to a lot of peripheral devices. The UARTs support rates as high as 5 Mbps.
So, what do you want to do with these building blocks? It's kind of up to you. One application I can imagine is a substantially less-sucky (compared to all the other ones out there based on MCUs) audio-frequency oscilloscope. The ADC sample rate is almost high enough to support it, particularly if you designed a decent front-end, and the analog comparators could be used to do interesting things with triggering (lots of MCUs try to fake it, badly, with software triggering).
The schematics of the board: <not yet released ?>
And a toolchain. Usually you work in C, TI has a tool based on eclipse and gcc, TI Code Composer Studio: http://www.ti.com/tool/ccstudio
BTW TI Stellaris MCU comes with some really good libraries that are included in ROM.
Usually what happens with this boards is that they're used for a lot of different projects by hackers. Expect to see a lot of activity in space like you can see on hackaday: http://hackaday.com/tag/launchpad/