I think they are not good for the seller, and heres how my logic works
lets say I want to sell a game, which sells for about £20 on a normal day,
lots of people wait for cheap listing days when one is due which means
many similar items finishing at the same time/ set of days 3/5/7/10 etc ,
5-6 people selling the same game, ending on the same day means it will probably go for £14 due to more opertunity for your limited number of buyers at that time
so I loose £6 to save myself 50p on listing fee
of course thes figures are all made up, but the principle is right I think... waht about you.
BTW, today (thur 21 apr 2005) is 5p listing day on ebay.co.uk if you want to take advantage/disadvantage.