The patch is mainly multiplayer focused, and is an attempt to deal with technical bugs that may have hindered progression or performance in the game.
The full patch notes can be read here, but if you lack the time or energy to go through the heftily detailed post, you can read on to get an idea of some of the major changes.
The patch mainly fixes the exploitation in the multiplayer that allowed players to become invincible, invisible, and/or fire rockets from standard weapons. The PC version of the patch will fix issues with Origin and key binding options, whereas the PS3 version will get improved game stability (preventing crashes), and also a fix to the invites. The Xbox 360 version will fix crashing issues during startup.
The Krogan Vanguard’s rage bonus now works properly. In addition, players who get disconnected during a gameplay can rejoin without having to reboot, and you cannot grab Geth Pyros over cover. You can, however, deal additional damage to tougher enemies like Geth Primes, Brutes, and even the Atlas by headshots or hitting sensitive regions / weak points.
The patch is expected to go live tomorrow.