Do you all remember the time when you tried highlighting your hair with lemon juice? I think I tried this when I was about 12 or 13 and my mom wouldn't let me use traditional hair color to lighten my dark hair. Here's a great how-to guide on highlighting your hair with lemon at any age:
http://www.hairstyle-blog.com/hair-highlighting-with-lemon-juice.html

I used lemon juice to lighten my hair when I was younger.  My hair was quite short (pixie) so the damage was not as noticable.  I would notice my hair getting straw-like, but that could also have been all the pool chemicals as well.  (I had 2 swim workouts a day - murder on hair!).  I wouldn't be willing to use the lemon juice on my hair now - too much at risk with hair as long as mine.