I remember not long ago seeing a lot of chatter in the ham community about large-scale "Broadband over Powerline" (BPL) systems causing harmful interference across several bands. Does similar interference happen with SOHO "Ethernet over Power" (usually called "HomePlug") networks?
HomePlug networking is a convenient way to extend home computer networks, when WiFi is impractical or undesired, without having to run cables across the house. However, I would not want to recommend this to anyone if it is a known RFI offender.
If these devices are known to cause RFI, is there anything the end-users can do to reduce or eliminate their impact without having to actually replace them?