The answer is never because:

• Network effect is too great, that is you can use them a lot more now than when it was at $1
• User base is greater, like a mmo, myspace, or similar social network there is always going to be at least some users even if the limelight fades. Case in point, myspace and friendster still have millions of users, even though they are considered obsolete/out of favor
• Too much investment has been made, there has been too much money and brain power investments to go back to the levels of $1