To what extent is gender an influencing factor on a speaker's language usage?

It is noteworthy that since the 1970's 'gender' has been a focal point for understanding language usage - particularly the different usages between men and women. A popular view which emerged in folk conversation most prominently during the 70's decade was the concept that men and women are complete opposites (as John Gray put it "Men are from Mars, Women are from Venus"). However, this concept is constantly being challenged by contemporary theories, such as those of Janet Hyde and Deborah Cameron's. Hyde theorises that there are actually more similarities than there are differences between the language use of men and women, and Cameron deems that language difference as a result of gender is a "myth".