is that you can change the feedback if 
necessary.  For example, as a seller you receive 
the payment and leave positive feedback - and 
then the buyer turns into a complete jerk and 
demands a refund, leaves you negative feedback 
for some unknown reason or whatever - you can 
make an adjustment to your initial feedback 
posting.

I wish ebay would find a way to do something 
similar, but I think that's quite unlikely. ~_~

Sheri