After buying 100Mbps fibre, a speed test result shows that the fibre is only about 50Mbps. This is because the wireless router is slowing it down. To fix this, log onto your router and change the bandwidth of the wireless to 40Mhz instead of 20Mhz. This will increase the speed of your wireless.
You may also find that your fibre is not as fast as it should be because you are connected to a wireless b or g router. Buy a wireless N router which will be able to deliver speeds above 50Mbps.