ADSLGuide has done a nice little summary of broadband ADSL line interference problems and the impact it's having on speed, especially following the introduction of BT’s MAX ("up to" 8Mbps) technology:


The piece also highlights an interesting article (here), which looks at similar problems that could impact future VDSL2 technology (if it ever sees the light of day) and their potential solutions.

The article reminds people to make sure that a Microfilter (splitter) is installed on every extension to the line your ADSL connection uses. Most ISP’s will tell you this, yet not everybody understands the importance of actually doing so.