I've started trying to AH materials I've stockpiled that I don't plan on using, figuring anything over the abysmal merchant offer for them is worthwhile. The problem is that posting 10 of a material for 24 hours at a 500 crown buyout can have a 750 crown listing fee. Sure, I get the fee back if it sells, but it seems unreasonable for the fee to be higher than my buyout price. I think the fee should either use the current formula or half the buyout price, whichever is lower (with some floor set at a fraction of the current formula).
Changing the posting fee like this should have little effect on gear/recipe auctions, as those are generally one item at a time and at a much higher price per item.
The listing fee is stupidly high on the AH. There are many materials where the listing fee is MUCH higher than amount you can ever expect to get for them. So, if the item doesn't sell the very first time, you will never have a chance to break even. You can easily tie up twice as much in listing fees as you will get in the sell price, which means that poorer players have a harder time using the AH to make crowns.
With the ability to sort stuff, and the fact that most items on the AH are commodities (that is, your light shards are exactly the same as my light shards, ergo it doesn't matter which get bought), there isn't a good reason to have a listing fee. Listing fees are important in physical auctions since there is limited space in real auction houses. Listing fees are also important when there are always physical differences between items (that is, your mickey mantle baseball card will *NOT* be exactly the same as mine), so buyers have to carefully inspect each item up for auction. Even at the height of the steam player rush when there was 3 times as many items listed on the AH, there weren't complaints about having too many items on the AH.
On the other hand, the mat sinks are so incredibly out of balance that if OOO made the AH useful, the prices of almost everything would drop to vendor prices.