Eek - does that mean the signal leaks out to (some of) the neighbours?
It depends on how your local mains is wired up.
If your mains goes from the substation the daisy chains from house to house then possibly, in my area all the houses are connected directly to the sub station and so the chance of picking up a signal is very low indeed.
In my house it is completely impractical to wire the house due to the layout and so homeplugs are a good way just to get a basic connection to the other rooms of the house.
I use D-link and they are very good indeed.
As for interferrence look up the Intel white paper on how USB 3 emits interferrence on the 2.4 GHz spectrum and then ask how that managed to get by regulations as that is going to play merry hell with a lot more people than home plugs will.
Edited by deleted (Wed 05-Jun-13 22:34:26)