I tried to write as small as I could with the means available (a pencil and copy paper), and this is what came of it:

tiny writing

The Euro-Cent was scanned at the same resolution as the paper with the writing. Its diameter is 16.25mm (about 2/3rds of an inch), which makes the letters about 0.34mm high (or 0.96 points). 1/74th of an inch.

Somehow, I just wrote something smaller than 1pt type. Blows my mind.

Added Friday, Jan 19th:
With denser paper, I managed to go even smaller:

smallest type ever

These letters are about .21, .22mm tall (0.6pt, 1/120th of an inch). "TO READ" looks good, but I fucked up TRY and THIS a bit.