The removal of OtherOS was one of the most controversial things Sony ever did with the PS3, so some hackers have put it back. Because of choice, damn it!
According to PS3 hacker and cop-magnet Graf Chokolo, OtherOS++ can "read or write anything" and is "very useful" for HV hacking. It exploits an older Firmware version and allows the user to control the PS3's memory and systems to a far greater degree than the original OtherOS feature.
Sony controversially removed OtherOS due to security concerns in March 2010. This removal has been used by certain hackers to pretty much justify anything they do. Because of CHOICE, damn it!
Hackers revive PS3 OtherOS feature [GI.biz]