I've been using Dr. Bronner's Liquid Castile Soap lately, and I heard that you had to use an acidic rinse after that, too. I don't think all soap bars are made with Castile Soap, but I've tried skipping my vinegar rinse after I wash my hair, and nothing has happened. It's no frizzier than it normally is! Since I've been ditching my ACV rinse lately (not so much because I'm lazy, but because I always get into the shower and forget to measure it all out beforehand!
), and nothing happened, I've come to the conclusion that it's not necessary. Maybe Kathy is onto something with the products and their pH's restoring the proper balance (although I'm no scientist!).