Firstly, the character is not called the "WTF character"; that was the title to the story that had the character as the topic. For a small background, that character is the bidirectional character that allows text to be written right to left. All Unicode editors display text following the character from right to left. The character is
The characters used are as follows:
0489;COMBINING CYRILLIC MILLIONS SIGN
202C;POP DIRECTIONAL FORMATTING
Though the character is seemingly harmless, it can have interesting side effects if inserted at appropriate places on the web. Sridhar's reddit tag cloud application was showing all tags in reverse as one of the articles had the article. That was when I started looking for places where the character could wreak havoc. Apparently, for HTML pages, the character seems to reverse all text following it in the inline tags. On encountering a block element, the reversing effect ceases.
I first tried this as the display name on Orkut. As orkut appends profile visitors as a SPAN, the names that followed mine were reversed !! On meebo, the moment you enter it in a chat room all converstations reversed ! On Yahoo Mail beta, I could hit the "To" field in revieved mails if one of my contacts had the character as a mail alias. Google search definately fails.
Though this is no real threat, it sure is a fun way to reverse contest of websites, leaving the other users wondering about the reason !!