I picked up a pair of Route 7 bib shorts from 1-day.com.au the other day - its operators seem to own the torpedo7 site. They had their first outing tonight, and seem pretty good for $30. Quite a few bike-related items seem to have come up there lately, so the RSS feed is worth subscribing to.
Bib shorts are great. I started out in regular shorts but literally havent worn them again since getting my first bibs. I found they stay in place so much better, no sliding down at all when you shift about. Only disadvantage is potential to get hotter as they do cover your abdomen more then regular shorts. Better pairs have mesh type straps that help alleviate this.
Normal tops are worn with them, just dont ever make the mistake of putting the bib straps over your top!! Its bib first, shirt second!
The benefits are that they can't slip down, thanks to the straps, there's no elastic in the waist, which makes them much more comfortable, and there's no possibility of showing a hideous piece of flesh below the edge of your jersey!
The drawbacks are that taking nature breaks in them is harder for us (depending on how low they're cut in front), and impossible for women, and cost. I'm happy with the $50 dhb ones I usually buy from wiggle, though, and Nalini's cheapest are sometimes offered for as little as $20. I found them crap, though.
They make no difference to jerseys, but your undershirt (if you're wearing one) goes beneath bibs so that it can be tucked inside.