Though the Academy has officially announced that Adele will be singing "Skyfall" (her first time performing it live) on Hollywood's High Holy Night, we still don't technically know if there will be Best Original Song performances as there often used to be on Oscar night. The Academy had previously announced a 50th anniversary celebration of the James Bond franchise and it's probable that Adele's soulful warbling will be folded into that, whether or not the whole category is represented. We also don't know if she'll be singing before or after her Oscar win*.
There's also been rumors that some permutation of the Les Misérables cast will be performing live but unless they're doing a choral version of "Suddenly", that doesn't necessarily equate to Best Original Song performances either since a cast performance sounds more like a "One Day More" type situation.
But, if you ask me, they'd be crazy not to just have five Original Song performances this year since that'd give you the opportunity to have four superstars on stage at various points: Scarlett Johansson ("Before My Time"), Adele ("Skyfall"), Norah Jones ("Everyone Needs a Best Friend") and Hugh Jackman ("Suddenly") plus a gorgeous little outreach for a little world music ("Pi's Lullaby") on the side.
I know that people think the Best Original Song category is silly but if you look back through the history of the Oscars it has often provided great water-cooler moments or at least tuneful bathroom breaks.
*the night's biggest lock?