i don't have a problem climbing with someone who only uses nuts. good nut placements are bomber, and i often find them just as quick (if not sometimes quicker) to place as a cam. some of you fuckers are so lazy!
i followed a number of climbs before i started leading. you can get an pretty good idea of what the placements should look/feel like that way. you can also have others follow you and critique. i am always surprised at how shitty some people's gear placements are, though! and like somebody up there said, aid climbing can be a great way to learn about placing gear.
oh, and if you don't feel comfortable putting your weight on a piece statically, adjust it until you do! they're not for looks ...