- You can only take as much as you need
- You cannot ask for data for one thing and use it for another
- You have to clearly state what data you will use for what purpose
- The opt-in has to be distinct from other opt-ins (so, 100 pages of EULA and then a checkbox "I accept" doesn't cut it)
The only problem here is that the penalities for breaking the data protection laws aren't very high .. I'd like to see percentages of a companies revenue.