It also depends on the straightening iron. I used straightening irons quite a bit in the past; I used to wear the "shoulder length straight bob" look. I didn't suffer any damage from that. However, one time I was 'swayed' into purchasing one of those high heat straighters from a kiosk at the mall and it burnt my hair. On my left side and in my bangs, I had patches of severely damaged hair. It was horrible.

Also, if you're going to straighten your hair you want to make sure to get a really good cut. When I had a great cut, my straightened hair looks awesome all day. I could comb it with a regular comb and everything (since when is a "curly girl" ever able to comb her hair?) and it always looked great. Later on, when I didn't have as good a cut, I could never get it to look right at all when straightening. The cut made all the difference in the world.
Attached Thumbnails
How bad is straightening?-angela.jpg