Now no one is suggesting that mathematics has been wrong for the last few thousand years. Don't worry pi still has a value of 3.14159265... If you look at the formulas where pi is used though you'll find something interesting. More often than not you see 2pi (2 times pi). Maybe we should be using a value of 6.28318531... instead.
pi is Wrong! (pdf) by Bob Palais is where the idea hit the web first. Bob suggested a new symbol that looked like pi but has a 3rd leg in the middle to represent twice pi.
The problem is that a completely new symbol isn't available on any computer system and would take quite a while to become widely adopted.
Michael Hartl took up the cause of twice pi and decided to use an otherwise underutilized symbol. The letter tau. The Tau Manifesto is a lengthy explanation of why twice pi is much more useful than pi is. Filled with examples and derivations it is a useful starting point to incorporate the tau in your mathematics. Tau, or even just twice pi with any symbol, may never catch on. Sometimes the most rational and clear headed ideas get ignored and can't replace current conventions.
We'll just have to wait and see if tau starts gaining traction.