If your router has gigabit ports then you won't see a gain. For example, since my router messed up I'm using an old router that only has 100Mb speeds. When the switch gets here I'll wire the server and any hardwired connections to the gigabit switch, then connect the switch to the router. I'll see a gain(10x theoretical speed) by using the gigabit connection. This will not affect my internet speed because it doesn't come close to maxing the 100Mb cap of the router.
If my router had gigabit, I wouldn't notice a difference because I would already have gigabit connections running to all wired PC's. In that case, the switch would basically just expand your current connection threshold. Typical routers only have 4 LAN ports, adding a switch would bump you up from a max of 4 connected devices to 10 connected devices(10 instead of 12 because one port on the switch would connect to one port on the router, taking up 2 ports with no additional devices connected)
thanks for the clarification. apple airport extreme do have 3 gigabit ethernet ports. this means that i will not gain much benefit if i dont have devices that need the port.