Patently Apple uncovered the lawsuit, which was filed by Florida-based Operating Systems Solutions, LLC. The suit claims that Mac OS X violates "at least Claim 1" of patent RE40,092.
This claim states that it is:
"A method for fast booting a computer system, comprising the steps of: A. performing a power on self test (POST) of basic input output system (BIOS) when the system is powered on or reset is requested; B. checking whether a boot configuration information including a system booting state which was created while executing a previous normal booting process exists or not; C. storing the boot configuration information from execution of the POST operation before loading a graphic interface (GUI) program, based on the checking result; and D. loading the graphic user interface (GUI) program."
So who is Operating Systems Solutions? We were unable to find any information about the company not related to this lawsuit. It looks like this patent was originally granted to LG Electronics in 2002 and later reassigned (probably sold) to Protimus Technologies, LLC. It's unclear if Protimus Technologies is associated with Operating Systems Solutions or if it just sold the patents to the company.
Apple is no stranger to patent infringement lawsuits. The company is currently suing both Samsung and HTC over patents related to iOS.