Where in Europe? They certainly aren't here in Portugal nor in Spain, and I don't remember seeing them in Belgium, which I've visited recently.
As for the legality, I wouldn't be so sure. Owning them is certainly legal, but filming the public street indiscriminately is usually considered against the Data Protection Directive, and I don't see why would dashcams be excluded.
Across Europe. OK I guess 'ubiquitous' might be an overstatement, but I regularly see cars with dash cams in Belgium, The Netherlands, France and Germany, which is where I have driven the last few years. I can't find any Europe-wide actual sales data, but I don't see why there would be huge differences in other countries. Also, they're readily on sale in e.g. Spain, Portugal and Hungary (just 3 countries I checked). Which of course doesn't necessarily mean that they're being bought en mass, but which does give an indication.
I rarely see them, but I was told that stores do sell a few dashcam kits. I wish it was a standard practice, I couldn't care less about privacy, people are far too crazy on the roads, even on parking lots (I'd even buy 4 cams to cover all sides).
They might not be illegal here in Germany, but dash cam videos are regularly thrown out as evidence by courts. (And that's quite surprising, the bar is very high for that to happen in Germany. No fruit of the poisonous tree here.)
Sure, so what? They're still mass surveillance even when their footage is not distributed, or used in court. That's my whole point - surveillance that is kept secret is the real problem, and anyone with a few $k or less will be able to set up a vast surveillance database in a few years - very little of which is covered by laws today (yes, some countries require you to register yourself with the privacy watchdog if you hold records of people, but how would anyone check? They're mostly toothless today already, in many places)
