Appart from hearing that e-bay don't want to use them anymore:
I have a post box the local post office and over the last 3 months I have received mail for at least 12 differant people from 8 differant towns with the same post box number as mine but with their postal code and town being clearly visable.
If you put them back in the mail with the town and code highlighted they are back in your box the next time you take out mail.
Seeing that, one can only wonder how much of your mail goes elsewhere.