Unless you're incredible... or God - I feel that even the smallest amount of success in ANYTHING requires some preparation (even if it's minimal). Many people can't just graduate from nursing school
and take this test without some degree of studying... I can't say it hasn't been done, but it depends on the person, their education, and their ability to critically think.
I came across a lot of information studying for this test that I never remember learning in nursing school. Kaplan taught me a new way to think - which was required for the NCLEX. To properly prepare, you have to become familiar with the way the questions are asked on the test... not to mention, comprehend the material that makes up the basis of each individual question.
I would strongly recommend enrolling in a course. If not, I hear Saunders is a wonderful book. I took Kaplan and it taught me what I needed to know.
P.S. To sum it all up -- Any amount of studying will, no doubt, help you on this test, but no amount will ever convince you that you're prepared enough. (Maybe that's what your buddies meant?)