Recently purchased a house and found the performance of my 200Mb devices was rubbish, this combined with the requirements to stream HiDef content from my file server to the living room and bedroom the only option was to run CAT5e cable throughout the house (2 stories). Running the cable either through the dry wall or cavity was easy enough including a 2 floor drop from the loft space to the living room although it did take a few hours and a lot of patience to fish the cable out of the cavity if I am honest.
The install is NOT a cheap option, when you add the cable (never run 1 cable when 2,3, or 4 add some future proofing HDMI over cat5e/6) and the socket outlets which in the UK are upto £18 each for 2 gang 4 outlet EURO style in a metal finish (to match the other outlets).
There are also houses that dont have cavity walls or its a rented property that you can't run cables though the walls.
I still have the 200Mb devices and they work great for the internet radio which only needs very little bandwidth along with wireless for mobile access.
For some people without the knowledge to run some cables (although it is very easy and there is loads of info on the web to help) these are a very cheap option for plug and play internet access.