I have a MacBook Pro (newest model), I know it's not the best gaming computer but was wondering if anyone knew how CS performs on it so I don't waste my time and money if it's completely unplayable.
I believe that all source games are optimised to work on MacOS just fine. As long as your specs can handle it (which it most likely can if you're running one of the newer models). You should be fine.
It depends on the system itself. If it doesn't run well in the first place, don't expect miracles to happen. It doesn't take much to run Source Engine games these days, though.