But, I saw this tweet today with upside down text and could not figure out how it was done.
http://www.flipmytweet.com/ ʞuıl sıɥʇ ʍolloɟ sıɥʇ op oʇ ʍoɥ
Turns out to be an interesting trick, and really esoteric. They wrote a script that first reverses your text (abc becomes cba) and the substitutes each character with something that LOOKS like the upside down version of the letter.
So, the "h" for example, is substituted with the latin mu (wait, that's not mu.. damn, can't remember my Greek alphabet...). Some are easier, like d becomes p and visa versa.
Of course, in this era of search engine optimization and text messaging, I wouldn't want to rely on a mix of Unicode and ascii text, but then again, I doubt whoever figured this out was really interested in conforming to standards.