some people have different experiences, but ive had a white 3g since a month after launch and i can say ive had horrible experiences.
the very first 3g i bought, i also bought a case with it. the apple specialist picked it out, and gave it to me to put it on. i had difficulty with it, so he tried putting it on. here the case was fit for the original iphone, so when he got it on. we all heard a crack, and the entire backing broke in half. he offered (very very very willingly) to replace it, and came from the back with another white iphone 3g box. he set me up and as i was putting on the right fit case, i noticed multiple small cracks along the headphone, volume rocker, and camera. he again replaced the phone, very embarassed.
since then, ive replaced my phone 4 more times due to small hairline cracks gone crazy. every time i went into apple, they stated it was minor and not enough to warrant an exchange. a week later, i would come back with the same hairline fracture gone crazy. for example, one time the crack was stemming out of the camera. the genius told me they couldnt exchange something so small, so i said ok. 4 days later i woke up, and the entire camera and casing were apart. i mean a good 2-3 mm distance apart, with cracks everywhere. that was my latest exchange. now, i have cracks on the silent button that doesnt work. apple wont replace this one, though.
sorry for that rant, but its unbelievable that the 3g build quality is so terrible. i have 3 3g's on my family plan, and i pay close to $300 after taxes to att monthly. whereas, my gf and her family of 4 iphone 2g's went to tmobile. they pay a fraction of what i do, and they have better phones. its not worth it at all.