When will Barack Obama's portrait replace Abraham Lincoln on the US 5 dollar bill?

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Regardless of any rumors circulating on the internet, it would be decades if ever before President Obama's portrait would appear on a coin or bill.

First, by both custom and law no living person can be depicted on circulating currency without a special act of Congress. Even the Presidential Dollar series of coins is scheduled to skip over any current or former president who's still alive when their turn comes to be depicted.

Second, this claim was fueled by a satirical article posted on a humor website that was illustrated with Photoshopped mockups of bills featuring various people including President Obama. Despite other stories such as "aliens meeting with Mitt Romney", very few visitors realized it was actually a satirical site and even fewer bothered to perform basic fact-checking. The story spread among many conservative web pages and Talk Shows, gaining an air of (false) legitimacy in the process.

Third, with the exception of the rush to memorialize JFK on the half dollar in 1963, the decision to depict any president or other individual usually takes many years, until their place in history has been more or less settled. Given that Lincoln is considered by many historians to have been our single greatest leader it's very unlikely that any other person would replace him on the five except as part of a full redesign of all currency. Given the resistance of Congress over the last 40 years to allowing anything but the most minor changes to currency, that's unlikely to happen in our lifetimes.