I can only speak for the use of Flarm where I fly in Switzerland.
At my homebase all gliders, microlights and rescue helicopters have it fitted. There is some scepticism amongst the 'Lycoming' flyers which is unfortunate.
Flarm is GPS based; all pylons, masts and aerial cables are in its database. Anybody can add new obstacles by sending their coordinates to the developers.
It can be linked to PDA devices such as Pocket FMS or SeeYou Mobile to give a map based display of threats with voice warning.
Fitting of Flarm is partially subsidised by aviation insurance companies in Switzerland.