@Gordon I'm having mixed success with the HID code here, using your simple Keyboard Hello World with the firmware from 15th July.
It doesn't work at all on Windows 8.1 64-bit. I never see any characters appear. Tried a variety of hubs and directly plugged in.
On OSX, it acted very strangely with context menus popping up randomly, until I removed the setModifiers calls. Now it works every few button presses but also sends the last character repeatedly on many attempts.
However I'm thrilled to get some code running which turns the Pico into a OTP Fob and successfully generates the same codes as Google Authenticator for one of my logins. If the USB HID code worked every time, then the Pico would be as good as a YubiKey :-)