Privacy rights are not that much of an issue until you don't use it a widely and publicly open system like Facebook is.
I admit I don't have (much) of knowledge about privacy law in other EU countries, but in our, things are not that simple.
Sure if you are using this at home, things are easy, and noone will really care about this (as long as you don't put this out to public), therefore noone will bother to come and check what you are running, and how you are using your tihngs. But considering not everyone are using this at home, but quite few of us are running PM for business in offices of registered companies, we are tied to some stricter control.
For companies, even if you don't use this database publicly, you are limited what kind of data you can collect (they actually do send inspectors to check these things from time to time). And collecting such data is way out of limits, no matter what your usage is. I know it sounds stupid, but unfortunately that's what we have here (Slovenia).