The wireless internet on my Mac became extremely slow recently on my 27" IMac. I don't recall doing anything different other than doing the Apple Software updates which I let it pop up and install automatically. On my Mac Book internet is still fine so I don't think it's the model or the router.
I'm not sure where to start digging the cause of this or how to solve it. Looking into the System Preferences on my IMac, it's pretty identical to my MacBook!