i don't care. doesn't bother me. however, my own bra straps showing would only be ok if i were not wearing a shirt that could easily cover them. i freak out if i realize my bra strap is showing with a long sleeve shirt, but with spaghetti straps, the only way around it is to not wear a bra. i'd only wear black or colored bras if i knew they were going to show.
and seeing people's thongs absolutely disgusts me. the tops of other regular underwear i wouldn't mind, but i only ever see thongs sticking out.