At about 40-45 meters the signal starts to fade some. But the ethernet cable should substain a good signal about a 150m-180m run before you need to start boosting the signal with a repeater.
The maximum cat5 cable length is 100 meters or 364ft.
Originally Posted by Drakan290
Yep 100m is what the IEEE has said the maximum cable length is.
You may get signal further than 100m, but don't expect it to be reliable.
Now, for the next question that I'm sure will come up... How do ISPs communicate between hubs!?
The answer lies in fiber and analog... Coaxial cable, fiber optic are the two most common forms, and they can go many miles before signal degredation.