wow I'm so glad i didn't get a white one. and the dirt is so noticeable in the seam around the sim tray. my black iPhone is crack free. only a few scratches 
It could have something to do with production times maybe? Like mine is 28 week white iPhone with no cracks at all... even after my phone took a tumble last night when part of my computer table (the part holding the keyboard) fell off. I've inspected it all over and found no scratches or cracks.
MB499LL no cracks.
Same here made week 28. When was yours made? And when did you purchase it?
Week 30, purchased July 28th.
A problem is discovered with the new 3G iPhone and people are so quick to jump out and say:
"I'm glad I stayed my aluminum original iPhone!"
"Who needs 3G anyway!"
"At least this metal backing won't crack!"
I think those people are just trying to make themselves feel better because they have the older phone. You know darn well if there was a 1:1 swap from Apple you'd do it in a heartbeat.