In my house is an older black macbook. If I plug it into the house ethernet with a cable, youtube videos pause and spin the throbber and other network operations are also sluggish.
If I disconnect the cable and turn on WiFi, all is well. The TimeCapsule supplying the WiFi plugins into the same hub as the aforementioned cable (though there are many more feet of wiring involved).
Is there an log on Lion that would tell me if the ethernet interface was getting errors, or getting sick?