when you are leaving feedback you will be asked to 'star' rate the seller on some aspects of the transaction.  These Detailed Seller Ratings (DSR) are out of 5.  There are four ratings:  These are:

    Item as described

    Communication

    Postage time

    Postage and handling charges

Now, if an item had 'free postage' then the rating for that item for the last DSR will automatically be 5 stars.

There is some automatic rating for Communication but i am not sure of when Communication is auto rated.

IMPORTANT: 'Postage time' IS NOT the time it took for the item to get from the seller to you.  You are rating the seller and not Australia Post or any other carrier.

The DSR ratings you leave will not be made known to the the seller.  However, some sellers are able to work out the ratings left by individual buyers if they monitor their DSR average ratings very closely.

Some time back a poster posted on the boards that when they first joined eBay they thought that a rating of 4/5 was a good rating to leave.  They commented that they quickly learned that this is not the case.  Ratings less than 5 will impact on a seller, so unless something was bad about a transaction you should consider leaving straight 5's.  If you ever think that a seller deserves a 1 or a 2 for one of the DSR's you should not make that decision hastily.