I know I'm bringing up an old topic, but I decided to ruffly some feathers. 
When I was a scout our troop happened to not have any female leaders. In Cub Scouts I only had male DLs and CMs. When I was a 19yo young adult scout leader, we had our first female leader in the troop. It definitely changed the dynamics. Sometimes boys need to be boys, and having a mom around changed the dynamic significantly.
Our chartered organization is very much in support of the dads working with their boys. All of our direct contact leaders are men. Part of me just says that when teaching boys to be men, there's something that women can't do. They can't show the boys how to be men. Other packs are different, and that's wonderful – just like each boy is different, each pack is too. Women have given a lot to the BSA over the years (my mom serves on a district committee). I support the BSA's policy to allow women to serve in any position their chartered organization approves them to serve in.
On girls in units: I like how the BSA has set up the system. Single option from 6-18, and for those high adventure times at 14-21 co-ed. I know that at least at one point, Scouts Canada was set up along similar lines (single-gender until 14, co-ed after that). I like our system where there's a single-gender option until 18 better. Like I said, sometimes boys just need to be boys. In fact, if the GSUSA wasn't so screwed up it'd be a perfect setup, with parallel single-gender options.