I gave a book talk on Buddy System at Barnes and Noble at the Baltimore Inner Harbor over the weekend. The question again came up about opposite sex friendships.
Yes, men and women can be friends but I have learned great variation exists in the ability to maintain friends based on culture and age. Western and first-world cultures historically permit more contact between men and women in the workplace and socially. Age plays a huge part, too. Younger people are more apt to be single or, if partnered, to be more recently partnered than older people. They thus are transitioning from one relationship situation to the next and are eager to maintain friends they had of the opposite sex before they married or partnered. Older people have been out of the singles scene longer and were also raised during a time when sex roles were more restricted.
Sexual attraction does exist between some men and women in their opposite sex friendships. That is part of the excitement of their friendships. Other men feel more comfortable being friends with women to whom they have no sexual attraction - it feels safer and is less of a hassle. Friendships come in all shapes and sizes and can wax and wane as interests change.
Bottom line - grow as many friendships as you can - people with friends live longer, healthier lives.