I have to say that Unicode support on Twitter has been used for both the good (e.g. posting political protest messages in Persian (Iran) and other languages) and the silly (I ♥ you!)
A particularly interesting trend I just saw was the use of circled letters in a Twitter message. Can you imagine:
Ⓒⓘⓡⓒⓛⓔⓓ ⓛⓔⓣⓣⓔⓡⓢ ⓘⓝ ⓐ ⓣⓦⓔⓔⓣ!
For the record, you can find these chracters in the Unicode Math block from U+24B6 (Ⓐ CIRCLED LATIN CAPITAL LETTER A) to U+24E9 (ⓩ CIRCLED LATIN SMALL LETTER Z). There may also be negative versions (white letters in black circles) in the one of the Plane 1 CJK blocks, but these may not be widely supported. Apparently, it is so common that Droid has short codes (e.g. :m: = Ⓜ). I’ve been way to much of an introvert to have never seen this before now…
FYI – if you are on a Mac and own TextExpander, you can quickly import a set of abbreviations. This could be handy for midcentury retro art, but I hope I don’t have to read very long versions of these messages.