Informal mode of address

I'm reviewing German and noticed that you teach the informal mode of address, z.B., "du."

I recall that using "du" inappropriately was considered rude. Has that changed in German-speaking countries? 

Hi Scott,

There is definitely less hierarchy than there used to be, still I use "Sie" instead of "du" when not sure, especially with people who are a lot older than me. 

Regards

Paul