After looking at the prices some companies like motec charge for their entry level EFI management systems i've decided to start learning to tools of the trade. MCU's.
A mate of mine managed to hook me up with an Atmel STK500, which is nice MCU development board for much of Atmel's Atmega* range.
So so far i've had to learn

• Driving IO lines
• Interrupt driven programming (think of hardware operations triggering your function calls)
• ADC conversions
• Timing - Counting the number of cpu cycles in a PWM "pulse"

Mostly i' ve been using the ATMega163L Which has been replaced by ATMega16