I have the HH Big Mimi Quilted Satchel and it's not heavy at all... i can't figure out what metal the chains are made of, but they are SUPER lightweight... in fact, almost TOO much so in that when i first tore the bag out of the HH box, i thought the straps looked a little cheap...
i just saw this chain bag from Paul Smith for fall on nitrolicious.com (great blog for street fashion!) - i'm not sure i'd carry it but i love looking at it!