My first reaction was "who needs another one?" but after messing around with the site for a few minutes, it doesn't look half bad. You've got your standard item search, and one feature there I've never seen on other sites is the ability to do searches by what drops in each dungeon-- yes, on Wowhead and Thottbot, you can look up dungeon bosses to see what they drop, but whenever I'm trying to figure out what instance to run, the first thing I do is check WoWWiki to click on each of the boss names in one place and see what they drop. Having everything in the dungeon at a glance is pretty nice. (Update: Wowhead can do this) The other big item of note is that Lootables actually links to each of the other databases in its listings. I didn't see a place to put comments (which are a huge draw on the other databases), but considering all the comments about the item are just a few clicks away, maybe they decided they didn't need them. You can also use the colored boxes near each item to "store" it in a dialogue on the right sidebar, and the site remembers what items you put there, so item comparison is super easy. Very nice feature.
And the last thing I noticed that separates Lootables from other databases is that they've actually created leveling guides for all the professions, complete with links to all the recipes and items you need. Creating an item listing is one thing, but showing clearly how to use those items is definitely helpful.
Birgitte also said she was looking for feedback, so if you guys have it, let's hear it. The only real suggestion I have is to come up with some way for us to see the items-- so far, the best these databases have all come up with is to use user-submitted pictures, but surely there must be some way to both avoid legal pitholes with Blizzard and show us what the items look like.