Some people have mentioned here debugging with "well placed printf...".. Oh boys, come on... have you ever debugged any serious stuff?
Printf debugging (via SWO or UART or anything) is indeed helpful, but that only helps with software algoritmization issues. When it comes to fiddling with peripherals, printf becomes useless.
One nice and easy way for learnig how peripherals work, is just to take the debugger and play with the bits. Most peripherals can be learnt that way.. like RTC, ADC, USART, SPI, I2C (on the above mentioned F0 it should work fine)... And learning ARMs is mostly about the complex peripherals (NXP fanboys doesn't understand that, their peripherals are pretty straight)
dannyf: That's all about the ST's marketing people. StdPeriph was good, but the headquarters decided to abanon that, just because it is old (and maybe to much hard to use for arduino whiners - so more arduinistic library must have been made). Simply, marketing and engineering do not mix.
:-)