I used to have a homeplug network in my old house. I know they say you shouldn't use them on separate ring circuits but I didn't have much choice, so I wasn't hopeful it'd be any good but I was surprised to find they connected well and I'd get around 60mbps speed.
But, over time (about a year) they degraded in connection speed and quality to the point where they barely worked. Nothing really changed with the electricity usage in the house either and the homeplugs seemed to connect find if they were close together so I never did get to the bottom of why they worked really well to begin with but slowly degraded to the point of uselessness.
They were D-Link's homeplugs, I've always found D-Link tend to make good hardware (maybe I'm wrong about that though, I must admit I haven't used much of their stuff over the years but what I have used still works fine, except for these plugs which I've since thrown away).