The problems with powerline networking...
If you don't count the cost of powerline networking equipment, the interoperability issue and the possibility of radiating interference from powerlines, powerline networking has other problems.
All of this is really too bad, as powerline networking seems like an idea that would have a lot of promise, especially in older structures. I do have some powerline equipment, purchased at severe discount. It's a neat idea when it works.
In the US and Canada at least, electricity is delivered to most homes over two 120 volt lines. In a well planned electrical system, the electrical fixtures should be evenly split across these two. This creates a problem when a powerline networking device needs to communicate to a device that is on the other "hot" line. The signal has to go back out of the building, through the pole transformer and come back to "jump the phases". Oftentimes, this is just too much to ask of the signal and it can't be done reliably or at all. This problem can be overcome, by installing a "phase bridge" or supposedly (NOT verified -- check it yourself before you even THINK of trying it!) by placing a suitable capacitor across the two hot lines at your incoming service panel.
What about the other problems?
Cost...it seems like this gear is almost universally more expensive than it "should" be. The prices have dropped so on wired and wireless gear alike. I suspect that limited production of powerline gear, due to its limited demand, keeps the price up.
Interoperability...I know there are supposed to be standards, but they don't seem to hold up well even when pieces of equipment say they're "compatible" with one another.
Radiating interference...this one I'm less clear about. The powerline Ethernet devices are far from the first to use the powerline as a transmission medium...countless "wireless" intercom systems, X-10 devices, telephone line "extension" kits and probably too many things to name have all done this. Where was the outcry then? (Yes, I realize that these devices might operate at differing frequencies to the powerline Ethernet stuff, but I'll bet there is some chance of radiation taking place there as well.)
Back when I wired my (very old) home for networking the first time, powerline gear didn't exist and Wi-Fi didn't either. Later, when I upgraded everything from coaxial Ethernet to Cat5 and fast Ethernet, Wi-Fi was just starting to become available and I did not consider powerline connectivity equipment as an option, if it even existed. During that process, I can promise you that I used all kinds of interesting words and struggled with a lot of situations.
If I had to do it again, given the issues with powerline networking, the lack of interoperability and the cost...I'd definitely use Ethernet or Wi-Fi.