One of my Australian friends got married recently, and for weeks beforehand, all she could talk about were the upcoming stag and hen parties. She and her girlfriends and her groom and his buddies each planned out separate weekend getaways instead of having one-night-only bachelor and bachelorette parties. They had a great time, I gather there was a lot of drinking, relaxing, and debauchery for the bride to be and for her groom.
Personally, I'm not a big fan of single-sex parties. If I ever marry, I'd be happy to have a fun night (or weekend) with my partner and all our friends combined. A bachelorette party would probably make me crazy. I like to hang out with my boyfriend and I also have quite a few guy friends . . . it wouldn't feel like a party if they weren't included.