deskthority

Agree about the regulator. I think the main advantage is board space rather than cost (if you're making an ultra tiny USB dongle or something commercially).
some of the STM32F0 parts do crystal-less USB
Specifically, the STM32F0x2xxxx, so the STM32F042xxxx, STM32F072xxxx (out of the stm32f0 series ...

well...looks wireshark USB debugging works on Windows too:

http://desowin.org/usbpcap/

I would definitely prefer to use Wireshark for debugging since the interface is familiar / it's got lots of support if you have problems.

You can still use mbed offline if you like, see https://developer.mbed.org/handbook/Exporting-to-offline-toolchains

I should really try chibiOS some time, I've come across it before but wasn't sure whether many people used it/how often it was updated. I also didn't realize it supported so many ...

Edit: mbed usb is only supported for STM32F4XXX series :(. so please ignore the below.

Well, I don't think I need an RTOS or anything like that, and I'm actuallly interested in writing the keyboard parts of the code myself. I've done a fair bit of microcontroller programming, but mostly in ...