if you go to adslguide.org and go to the forums and search for talktalk there are lots of threads regarding this isp....unfortunately most of them appear to be negative or complaints.
In general because its a low cost 'free' ISP they do not have vast network capacity or the money required to extensively move the network forward, its run in a very cost effective manner which shows in its general overall performance and the general type of complaint aim towards it.