Like Martin I'm a customer of Zen internet, and just like him I've signed up for their faster (at no extra cost) ADSL service, no catch? Well there's two potential big catches, one I'm not necessarily going to get an 8Mbps connection, and secondly it could get rather expensive if I creep above the 20GByte/month download cap.
Martin has all the details on how to find out if your exchange is enabled yet for the faster service, mine isn't yet. One good thing is that my line appears to have pretty good signal strength and low noise (according to my router anyway), so I may be lucky enough to get a good fat pipe.
One thing to remember though is that this is still pretty slow and expensive compared to much of the world, however the good thing is that the UK is pretty well connected and it's not hamstrung by limited bandwidth to the outside world like the Iberian peninsular or the Antipodes.