The internet has changed that. Now, fans who would have normally encountered slash after first being part of the writing community for some time, can find archives with a few clicks of the mouse. There is slash on the internet for almost any show you can name. I even found one - I kid you not - for the Teenage Mutant Ninja Turtles.
What this means is that authorship has also changed in the past few years. While authors are still predominantly female, there are male slash authors out there - or at least, authors using male pseudonyms. The problem with the 'net is that it's so hard to verify anything. Although gay and lesbian authors are not the majority, they are certainly present. Slash has also expanded from the traditional "male/male" format to include "female/female" fiction, and many authors now seem to be writing and putting their works to the public at a much younger age - a lot of slash is now written by high school students.
That said, if you'd like to explore for yourself, here are some of the useful and/or interesting links that I found:
Slash Fiction on the Net: The most comprehensive list of slash sites that I managed to find, separated by subject. Very useful.
The Generic Slash Defense Form Letter: A message written by a slash writer (Susan Beth) to defend her hobby.
The Master/Apprentice Slash Archive: That archive I mentioned earlier... over 1500 stories about Obi-Wan Kenobi and Qui-Gon Jinn. This includes useful "interviews" with some of the slash authors.
The Foresmutters Project: A site attempting to archive some early Trek slash stories, and give a basic history of slash.
Minotaur's Sex Tips for Slash Writers: A slash "how to" guide. Quite in-depth detail.
X-Files University: Including the "School of Slashology".
The Star Trek Slash Ring: A web ring for Star Trek slash archives.
The Rare Slash Webring: With sites containing slash from obscure areas like Dead Poets Society, and, yes, here are the Teenage Mutant Ninja Turtles.
Minding One's Ps and Qs: Homoeroticism in Star Trek: The Next Generation: An article on ST:TNG, for those of you who want to see how the perceived themes carry onward...
The Zeal For Xena: Appropriation, Discursive Elaboration, And Identity Production In Lesbian Fan Fiction: An article on slash written by lesbians, with lesbian themes - as opposed to the male/male slash we've been talking about here.