Upside-down text (actually, rotated by π) appears to have been a hit last summer, but I've been seeing a bit on #python recently:

15:21 < lieuwe> dash: so how should i call decode on a possibly unsafe string?
15:25 < kerio> lieuwe: ɯǝןqoɹd ɐ ǝq ןןıʍ sıɥʇ ǝʞıן buıɥʇǝɯos

I though that was slick, so I looked around a bit today to see what people were doing in this regard (see the Wikipedia page for a list). Turns out to be a bit more complicated than I'd initially expected. The Unicode people apparently didn't see a need to methodically rotate characters, so while many have official "turned" forms (e.g. ɐ (U+0250) LATIN SMALL LETTER TURNED A), many others do not. The solution seems to be hunting around through the unicode tables looking for homoglyphs (which turns out to be an interesting phishing scheme in its own right).

Anyhow, none of the implementations I found addressed conversion of ASCII characters with the scope and formality I felt this important topic deserved, so I put together my own converter ;). ¡ʎoɾuƎ

Update: It seems that ikiwiki doesn't like UTF-8 filenames.

Update: As an April Fools joke this year, rotated its entire main page.