I did a week trip with 3 ladies to a cooking school in France. It was a fun, low key weekend. We cooked, ate, drank, gossiped, shopped for a week.
I have done few spa trips with girlfriends, and Norwich Spa is one of my favorites.
I think Montreal, Vancouver, wine country, Charleston, South Beach, finger lakes, Hamptons, etc are all great places for a getaway with friends, depending where you are and what you like to do. I think at the end of the day when friends get together they just want to have time/place to catch up.