What is this F-18 Hornet "air intake" for? I think I read once that they served to cool the on-board computer systems, but I'm not sure.
It's for keeping the boundary layer flow from entering the intake, it's called a splitter plate. I think it's done to prevent turbulence inside the turbine (prevent compressor stall) and to make sure the intake doesn't ingest slow air, to maximize efficiency.