I wasn't entirely convinced that networking over the mains would work in our house as we have three panels of power breakers protecting circuits in different parts of the house and some reports I have read in the past suggested that this would prevent networking over the mains from working. However, given that the wi-fi signal from a single BT home-hub system isn't strong enough to give good connectivity even halfway across the house, I thought I would give the Max Value 200Mbps Home Plugs a try as a last resort. As it turns out, this was a good move. Although we don't get 200Mbps from them, we do get in the region of 130Mbps, which is more than 10 times what the wi-fi managed previously. Basic installation was trivial - literally plug and play. Setting up security was done by guesswork as the printed instructions are so bad. I did this from an XP machine, so don't know whether it works on Vista. Inevitably, it was only after getting the security set up that I realised that better instructions about how to do this appear on the supplied CD.
You need to be aware that these units should not be plugged into blocks with surge protection, should not be near "noisy" devices etc, but also that they come supplied with very short network cables. Luckily, I have spare cables that are of decent length, otherwise I could never have reached my router from the plug units, but if you haven't got spare cables be prepared to buy some.
So, other than the short cables, I am very pleased with these units. They do what they say and have solved our home-networking without the expense of laying cables across the house.