I never pretend to be a writing expert. I do feel that after a few books, I've learned a couple of things along the way. Basing characters on people I know never seemed like a good idea, and therefore, I never did it. To begin with, I'm assuming there would always be a paranoia of someone 'discovering' that a character was strangely like them, not to mention hurt feelings, potential arguments, and maybe even a few Facebook rants...as much as we all love those.
Most importantly, I feel that characters create themselves. You might have a few ideas of who they are or what they're about, but in the end, characters tend to form as you write the story. It's kind of like having a child and assuming the personality you think they'll have; chances are, they'll soon show you that you never had a say in the first place.
Characters are complex. As a writer, you'll probably have a deeper understanding of your characters than most people in your life. You can see inside their heart and understand what makes them tick. This makes sense because you're on a long journey together.
The interesting thing about characters is that they often are a piece of you. Just like every songwriter inserts a piece of who they are in their songs, every author tends to do the same with their characters. It's not something you think about, but rather it just happens. Maybe one of your characters shares your fears in life or your fixation on a specific pet peeve. The characters are unique, but they're also you.
And really, isn't that what makes the writing process amazing?