I only have one pannier on my hybrid; I don't think I've had 30 lbs. in it, though, but I just am careful and so far, have never felt unbalanced. I bought a bunch of presents for the holidays, some ceramic stuff and rode home very gingerly last year.
If I am just doing errands, or meeting someone for lunch, I do dress differently. Not regular clothes (well sometimes on the top they look like regular clothes, but are shirts with some lycra or a hoodie or Shak), but more casual, commuter cycling clothes. I wear my Jonesware wool hiking pants and the shorts underneath, with my right leg in a band for colder rides and look very chic . In the summer, I tend to wear skorts for errand rides.