Interesting observation re: wish fulfillment. I tend to do that too, albeit not with slash. I was just thinking the other day about how many of my female characters have only brothers, and it's not that I hate my sister, but I've always wanted a brother or brothers, just to see what that dynamic would be like. Also, many of my characters tend to have non-traditionally feminine attributes and occupations, in part, I think, because sometimes it seems like there are just more limitations to being a woman. I'm sure there are lots of other common thread to my writing that I'm just not aware of yet.

*g* On a completely different tangent, are you in the market for a new fandom? I wholeheartedly recommend the Final Fantasy VII fandom. Especially with the movie that just came out, Advent Children, more people are coming to the fandom. There's lots of eye candy and ample slash opportunity....
Just thought I'd mention it ;).