I can get infinity - any great reason for switching from a decent broadband (apart form the huge speed increase) ? Currently pay just short of £30 a month, calls and line rental included.
It depends what you do and what youre getting now, for some its a godsend for others its just more bandwidth.
You tend to get better latency (ping times) which is good for online gaming, but its not a big difference if your already on a good broadband connection. Having a website respond or a download start 6 milliseconds quicker isnt going to be noticable
The main thing is the bandwidth, for people on say under 2mb connections, watching tv online might struggle, downloads may take an age, so youd really notice the internet start working properly. Also if youve got a number of adults/teenagers in your house you dont get slowed down by what other people are doing. Youd notice download speed if you downloaded movies/games for example, instead of a movie taking say 2 hours to download from itunes it could take <5 minutes.
If your computer is crap and slow, itll still be crap and slow. If some websites are particularly slow, theyll still be slow.
For me the main differences arere that you can have people watching iplayer in different rooms, while downloading, while someones playing online games. Occasionally I download a large file, like the Windows 8 test or Diablo3 beta and a 3gb file is down in 5 minutes. Its expensive though, especially when you factor in that what you pay to BT never seems to be close to what they say on their website.