i feel awkward when walking, and although i got a few comments about the way i walk in early high school, i haven't had anyone comment on it.... well there was one time when someone thought i was drunk in a bar, i had only had a couple of pints, but i guess they thought i walked weird. my posture, however, has gotten much better because of rowing. i no longer slouch, and it actually takes effort not to slouch, so i think that has helped my appearance.
as far as the way you walk being a turnoff to the opposite sex, i don't think it would have that much of an effect. it might turn away some really shallow people, but anyone who matters probably won't care.