I just sold something for $5 and because ebay currently requires you to put in a Paypal account I gave mine. The guy that bought the item paid using Paypal, and after fees, I'm left with $4.53 - that's a 9.4% charge.
Because ebay was doing something bizarre when I listed it, I put the item up as $5 with no postage when I really wanted to do $1 with $4 postage. The listing and final value fee came to a total of 76 cents. So assuming it really does only cost me exactly $4 to post, I'll lose 29 cents from the whole deal.
Paypal's terms and conditions specifically forbid you from having a surcharge for transactions carried out using it. If they don't remove the requirement as a result of the recent ACCC ruling, I recommend that everyone add a note to the item description saying that Paypal won't actually be accepted at all despite it being listed, and that they refuse the payments in the Paypal wossname.