u = you (personal pronoun, polite version of "jij" or "je") uw = your (possessive adjective, polite version of "jouw")
I have been living in The Netherlands for several months now, and I noticed that in some paper ads, or on some posters in shops or in my company, they rather use "je/jij" instead of "u". Only more formal docs, like administrative stuffs, are written with "u". I assume it must be more common to speak with a stranger using "je/jij" than using "u". It is strange because in France, we only use "vous" instead of "tu" when we speak to a stranger. May a Dutch guy can confirm it ?
Not Dutch by birth, but I've been here a good while. 'Je/jij' is definitely much more common here than the equivalent in France - I was fluent in French before I moved here and it felt really weird calling people I didn't know well 'je'. Now I automatically talk to most people, especially people my own age, with 'je/jij'. That said, when I meet someone new I find it's better to start with 'u' if they're older or it's a more formal setting (employer/employee, in-laws, etc.), just to be on the safe side. Myself, I get irritated when I ring up e.g. my mobile phone provider and they call me 'je' without asking. Dutch people are generally very quick to speak up if they prefer it less formal, so you're unlikely to get stuck using 'u' forever when it's not appropriate.
As a native Dutch speaker I can confirm this. A rule of thumb: use 'u' until the other person uses 'je/jij'. (If the other person is an adult.) Also, when using 'je/jij' it's best to stick to 'je' as much as possible, because 'jij' puts more emphasis on the fact that you don't use 'u'.