The dimensions are somewhat similar to British switches (might be even the screw spacing fits) but the mounting boxes are round, 68mm inner diameter, 74mm outer, 50mm deep (or 68mm for making splices).
That's a pretty typical one:
The mounting is standardized pretty much all across Europe except for Switzerland, Italy and the UK, either screws or two claws that spread against the box.
The system is fairly modular too, the rocker in the center has the shape of a receptacle or what ever you want to put there (Ethernet, TV, phone,...) and the outer frames are universal, available in single gang to 4 gang.
I have to admit I'm fascinated by the Vimar selection - they have EVRYTHING! And the larger boxes accomodate a lot of devices grouped together. For example you can have a Schuko socket and a switch in a box not much larger than a single Austrian switch.
Or even better... 9 Schuko receptacles and 3 switches or whatever in one box... or 21 switches... or 2 4-way switches in a box the size of a regular Austrian box... (here it's hard to get 2 3-way switches for such a box while in England they put in 3 of them).
Might be tempted to finish some place with the stuff - it ain't even that expensive, wholesale prices seem to be the same as Austrian.
They even have an English catalogue for those who're interested.http://www.elektrohaus.at/images/stories/pdf/vimar_general_catalogue.pdf