You mean wired network speed? On a mac, either the Network Utility (just switch to ethernet) or the Network applet under System Preferences (click the "Advanced" button, switch to Hardware tab) could tell you that.
Maybe there is a way to show wired network status in the menu bar like there is with wifi, I haven't succeeded, but if so you should be able to alt-click the icon for a quick and easy way to ascertain link speed. I'm not terribly down with the inner workings of OSX, I've only had a Mac since may this year. 🙂