Yesterday I got my reprap.me sanguinololu 1.3b - soldered the connectors, powered it up using a 1A 12V power supply(no steppers or stepper controllers attached), uploaded the firmware and made sure the thing communicates with Octoprint. All good.

However, I then left the board powered up for the night. This morning the IC1 was very, and I mean VERY hot on the board. Everything was still nice and functional but I powered it down just to be safe. Checked the power supply voltage, it's 14V without load. Could the extra 2V cause the 5V reg to grow hot?

Did you have both the 12V power supply and the USB connected? If yes, you might experience a problem related to the well known Sanguinololu bug documented in the wiki. If the regulator also gets that hot if no USB is connected, then it must be some other problem...

Yup, it was exactly that. Thanks!