Ps3 on Cinema display 27"

It comes down to know whether your Apple 27" Display is either the LED Cinema Display model or the newer Thunderbolt Display model. Does your Cinema Display come with a Thunderbolt port on the backside.?

http://www.apple.com/displays/

You can indeed use the LED Cinema Display as monitor for your PS3 with the help of this adapter:

http://www.kanexlive.com/xd

Please note, output is limited to 720p.

As stated at the kanex website, you can not use the 27" Thunderbolt Display as monitor for your PS3 with such adapter.

I just realized one of your tags for this question is 'thunderbolt', if that's your display I fear I know of no solution to this case.