Virgin Media's 50mbps broadband service is unlike anything you can experience in the UK right now. Unless you use expensive bonding services, you are unlikely to come even near that speed.
Obviously, using such a fast line to merely "browse" the internet and chat with your friends the old way would be equivalent to buying a Maserati to visit your neighbours next door; an utter loss of resources.
Alternatively, you could be using the £46 line for any (or all) of the below.
(1) Contribute to Megaupload or Rapidshare and Get free gifts
Virgin Media has already announced that it will be upping the ridiculously low 1.5mbps upload speed on the 50mbps soon. What you could then do is upload files on Megaupload or Rapidshare where you can earn reward points for each download successfully completed. There are no limits to the number of downloads you can upload. 150,000 downloads on Rapidshare earns you a 10.2px Samsung Digital Camera while 5 million downloads gets you a cool $10,000 (roughly £6600).
(2) Watch HD video on demand
Connect your computer to your super-duper 50-inch Plasma screen and watch HD movies in real time. Youtube, Dailymotion and Vuze. Youtube for example allows you to watch videos at up to 1280x720 pixels. The 50mbps line will also come handy once iPlayer (and other UK-based video on demand services) start broadcasting in HD.