This all depends on the student and how they feel towards you. I always want my kids to know they can talk to me about anything but if what they're telling me needs "higher" or more professional help, then i'd be quick to go about getting them that help. I think hanging out with your students outside of school can be very risky....especially while we're relatively close to them in age. I think the "professional boundary" you're referring to is one large gray area in the education system....we're expected to do so much and take on so many responsibilities...while at the same time if anything goes wrong, it's also our fault.
Dang, I'm good at getting off-subject. lol