PS3 firmware. And as previously promised, it's got 3D Blu-ray movie playback with it. According to the Official US PlayStation blog, there's also some added Facebook integration and new methods of grief reporting. We're still updating and will let you know what else we might unearth.
Update: Surprise, surprise, it works. We were able to test Blu-ray 3D out and got it running without too much hassle, as long as the HDMI setting is on "Auto" it will detect your 3DTV and switch to the correct mode just like it has for gaming since the update that enabled 3D functionality there. We didn't see any differences in the menus with the Disney Blu-ray 3D demo disc we had on hand, but we'll be checking out how BD-Java functions in 3D later on.
Update 2: Per Sony's v3.50 support page, and verified by several sources, the PS3 has to choose between Blu-ray 3D playback and lossless audio, whether from DTS-HD MA or Dolby TrueHD, it will fall back to a compressed codec while playing 3D content, while menus, items and BD-Java content "may be different" on the PS3 than on other systems.
[Thanks to everyone who sent this in]