I actually noticed a slight change in my curls when I STOPPED my birth control for a few months.
I had been on OrthoNovum 1/50 from the age of 17 'till about 25. My hair was it's normal curly self, botacelli and some ringlets, even. Then a new doctor switched me down to OrthoNovum 1/35 for the past couple years (I guess the 1/50 is the strongest stuff on the market... designed for people that are on meds that could counter-act the effectiveness of BC). My hair stayed the same, but my skin tended to break out a little more.
Then a few month's ago, my insurance changed, and during that annoying lapse, I just stopped taking it 'till things got sorted out. My skin has gone to hell, and my hair has gone beserko. It's become more unpredictable than anything. It will get oily out of the blue (the day I wash!) or will be ridiculously dry. I thought it was the weather, but my skin has been unpredictable, too! I'm going to start back up on the 1/35 this month, and keep an eye on both my skin and hair... hopefully I can remember to update in a few months....
I wonder if certain types of BC tend to effect things like your hair or skin more than other types?