My entry:

The coolest thing I've seen done with 3D printers so far is the built-in auto bed level calibration in Marlin firmware.
I'll talk ~5 minutes about the Holy Grail of home FFF 3D printers on the Budapest New Technology Meetup at 19:00 CET, today. That presentation describes my dream setup. Here're the slides: meetup-3dprint-szent-gral.pdf