Unless you spent your childhood under a rock, chances are you grew up playing with Lego at some point. In earlier years, it was more about different combinations of bricks and "special pieces" before LEGO came out with themed sets such as LEGO Star Wars or LEGO CITY.
I had no problems using my imagination to build girly things like dollhouses or horse stables, but then again that was way before anyone had ever heard of Star Wars or Harry Potter. Yes, it was *that* long ago.
Even though most LEGO sets are not specifically targeted at boys, it's obvious that most of them do not initially appeal to girls. This was quite unfortunate because building stuff is nurturing great imaginative and creative play, which would benefit girls just as much as boys. LEGO Friends have finally corrected this imbalance with a whole range of products that appeal even to the girliest of girls, and this might even entice them to explore the endless creative playing opportunity of building sets.