An Ethernet workstation can send data only when no other workstation is talking on the network. If the workstaiton transmits data and hears another doing the same, it assumes the transmission collided and data was lost. Each station then waits a random amount of time and tries to send its packet again. As more people try to use the network, the number of collisions, errors, and subsequent retransmissions grows quickly. Networks will slow down at an exponential rate.
Files take longer to print, applications take longer to open, and users are forced to wait.
Gigabit ethernet is here and runs at 1000 Mbps.