Some Americans love to wear them. Italians abhor them.
I love them. In fact, once spring comes and its too warm for them I feel naked. I also like they way it defines my neck. But that's just me. One important tip: Get new ones every year! It's easy to find good inexpensive white T-shirts and if you must wear them, there is no excuse for having a yellowed T-shirt peeking out of your shirt. Use last year's for dust and cleaning rags. Really.
As committed as I am to the white T-shirt under the button-down there are guys equally against it. What do you think?