a research team at Osaka University has "written" the letters "Si" using an atomic pen that interchanges silicon and tin atoms, enabling those who have the time, resources, and patience to manipulate said atoms one by one. The results are a diminutive 2 x 2 nm (or 40,000 times smaller than a strand of hair) which took about an hour and a half to complete.
That's impressive and all, but I once had an Asian lady write my whole name on a grain of rice at the mall. Suck on that one, scientists!
Atomic pen achieves invisible victory [engadget]
Thanks to mkaggie, who can actually write with individual electrons.