I swear to you wearing buns tore my ends up! In 2003, I went to the hairdresser with the crown portion of my hair much shorter than the rest and horrible split ends. My hairdresser's diagnosis: extrememly dry hair combined with buns, barrettes, etc. = breakage and split ends. He told me to, "moisturize, moisturize, moisture" and stay away from buns, elastics, etc. He was SO right.
Now, my hair is longer than I thought possible. I get occasional split ends (and trim them [and "end-of-the-line" knots] myself when they pop up. Not every one is the same, but for me, I found that staying away from buns was a HUGE step towards improving my hair.