Being a student pilot in San Diego, I use 122.75 every time I fly.
It is used in regions such as: San Diego Coastal, San Diego East, and San Diego North.
Yes, it is true that we use it to announce aerobatic intentions, but it goes beyond that. It also is not exclusively for fixed-wing aircraft, because both fixed-wing and rotor craft need to know each others intentions.
VFR traffic generally uses it to let other aircraft know what their intentions are. ex: "San Diego Coastal, Cessna 739MH, over Del Mar 3,500ft northbound, San Diego Coastal." or, "San Diego East, Piper Warrior 223F, over El Cap 5,700ft stalls, San Diego East."
If there is another aircraft in the vicinity, and they heard the transmission, they will respond with their information, and coordinate with the pilot to ensure they remain clear of each other.
Sometimes, you may hear chit-chat between pilots, but most are kind enough not to hog the frequency or step on other pilots. You will also hear pilots who are flying in formation using this to communicate with each other.
Also, 122.75 is only an Air to Air frequency. There is no ground entity that uses it to communicate with aircraft. From my experience with an aviation scanner, the reception of this channel can be very poor, as its not bouncing off any repeaters or ATCT's.
Hope this helps clear it up,
seven-tree-niner-mike-hotel