I grew up in Rapid City and I am really glad that I did. It is the perfect size and you can easily get to know everyone through sports, school, activities, etc. It is not unusual for me to see someone I know everyday when I run my errands or if I go out at night. The schools here are great too. I went to the Catholic school, but public schools are really nice and I have many friends from various schools in Rapid City.
The population here is about 80,000 with 140,000 in surrounding. The Black Hills offer
TONS of activity year round (hiking, climbing, biking, skiing, snowmobiling, fishing, etc.). Shopping isn't too bad here and we're getting a second mall that is slated for October. There are 4 theaters, tons of restaurats both local and chains, the Black Hills Symphony, Rushmore Thunder Hockey, fun summer festivals and events.
The Rushmore Plaza Civic Center is expanding to build a second Grand Arena with skyboxes to house the Rapid City Rush, a pro hockey team.
Rapid City is a fun place to live and I hope you consider it!