I was issued a pseudo-challenge to see if I could solder super-tiny 0402 (0.4mm x 0.2mm) SMD LEDs. They are about the size of a speck of dust and pretty easy to lose even sitting right in front of you. You need super-fine tweezers to even pick these up, but don't apply too much pressure and the LED may go flying, never to be seen again.
I was able to get not one but two LEDs soldered to strips of copper tape placed very closely together with gobs on solder on them. To illuminate the LEDs, I decided to build a joule thief on the index card with all the components super-glued to the card. It works really well, actually. I labeled the parts on the card. Now it's my joule thief reference card!