While the Auction House has been up and down while Blizzard works to improve its performance, a major new feature added in The War Within is the ability to limit search results to items from the current expansion!
Particularly useful for players searching ubiquitous items such as enchants, consumables, or crafting materials, the filter does exactly what it sounds like — removing results for items from previous expansions, so that you don't accidentally buy 100 Refreshing Healing Potion when you meant to purchase Algari Healing Potion instead.
For example, searching for a crafting «missive» without the filter returns all of the now unwanted Dragonflight results, while the filter narrows it down to just those used by Khaz Algar crafting in The War Within. Similarly, searching «potion» still gives a fair number of results, but no where near the amount of scrolling when including items from previous expansions!
Overall, it's a great feature that makes navigating the ever expanding list of player sold items significantly easier, and the only real downside of the feature is that it does not have sticky settings.