I have an Insteon starter kit (tabletop controller, 2 RF links, 2 lamp modules) on loan from a Home Automation dealer. I set it up a few days ago and will test it over the next couple of weeks, posting a review here and adding to it as the test progresses. A final review will be published on my web page.
My residence is not particularly friendly to either PLC or RF. The building dates from the 1950's. It has a brick exterior with plaster on all interior walls and ceilings. There's a lot of wire lathe. It has hot water heat with large metal radiator covers in each room. Initially, the main floor had two apartments. At some point they were combined into one large apartment (3BR,2 Baths, WBFP, formal DR, eat-in kitchen, walk-in pantry) and there are still two electric meters with no communication between the two sections.
With X-10, I've used two transceivers to reach both sections and use a Pronto (converted to send 310MHz RF), palmpads and stick-a-switches to control things. Since Insteon takes more or less the same basic approach, this should provide a good test bed.
My (pre-ELK) ESM1 shows the 131.65KHz Insteon PLC signal. I'm not sure whether it gives an accurate reading of the amplitude as it's nearly always fullscale. Of course, there's no way to determine whether the signal is good or bad but it does provide a quick confirmation that Insteon is putting something on the line. When the signal is sent to the local phase (i.e. local to the tabletop controller) the signal lasts only half as long as when it's sent to the other phase so it's obvious that the second RF link repeats the signal after the initial signal completes. The signals seem to be somewhat slower and to last much longer than the specs would indicate. Later I'll put my scope on the powerline to get some screenshots of the actual signals.
Unfortunately, I do not have an RF receiver module for the frequency range they use.
Personally, I find the bright bluish-white LEDs annoying - they are too bright. YMMV.
I also find the "beeps" whenever a button is pressed annoying. If I were planning to use this permanently, I'd have already put my wire-cutters to work. ;)