Here are a few answers. I'll edit with more later.
How does PIN entry work ? Like setting the time on your oven ?
Yes. PIN entry is on device.
Are passphrases supported ?
It's supported on the firmware but there is no UI to enter the passphrase on the device. So right now it's not implemented (it'll be on the Ledger Blue, which has a touch screen)
How are seeds generated ? Just like HW.1 by the chrome app ?
Does seed generation use 2 sources of entropy ?
Is the mnemonic seed generated on the hardware wallet and exclusively displayed on the OLED screen ? Or on the chrome wallet extension like HW.1 ?
How does mnemonic seed recovery work ?
Seeds are generated by the device on device. It never goes out. Backup and recovery are done 100% on device. You enter words with a clever mechanism of prediction; it's a little bit painful for 24 words but still really doable (and you won't do that a lot).
Entropy comes for the cryptographically secure generator on board; but you can always generate a seed yourself and recover it with the words.
Out of the box does Ledger S work with mycelium/electrum or will they need updates ?
It'll need updates.
What happens after 3 incorrect PIN attempts ? Will Ledger S share the power cycle requirement between PIN attempts ?
Secrets are wiped. You need to powercycle between each wrong PIN attempt.
Will a new udev rule be required for *nix ?
What are the specs of the STM chip ?
Where are the apps stored ? On the STM ?
What source code of Ledger S is available to review ?
What's closed source/NDA and unavailable ?
Will come back to you
When's shipping?
July 29th 2016
Do you have a video of S in action ?
Not yet