By the time I was about
twelve - so
ten years ago now, they had just started accepting
girls into the
Scouts as standard. I am talking here about the
Scout Movement in the
UK - I am not sure of the
US situation.
Incidentally, about this time, they also radically changed the uniform from shirts to sweaters. I think the whole UK movement was going through a rethink.
Anyway, it turned out that girls everywhere were bored of the stuff they were doing in the Girl Guides (cooking, sewing et al) and wanted to join the Scouts to do cool stuff with knots and axes - and who can blame them?
Of course guys couldn't join the Guides - but who wanted to? And Scouts was already mixed-gender at the Venture Scout level before then anyway. I don't think there was an equivalent for older Guides (17/18+) anyway. Equally, as far I know, Brownies and Cub Scouts (the age groups below Scouts/Guides) are still only for girls and boys respectively.
I never regretted having girls in our Troop, as one is just at the age when girls become nice - but it did make knowing where to grab someone during games of British bulldog that much harder :)