This concept has since been expanded and applied to just about every class, and there are many add-ons and sites that support item rankings, including (but not limited to) Loot Rank, Shadow Panther, Pawn, and Rawr. Wowhead has implemented both customizable and built-in item value scales, and seems to have some very sensible defaults for the various classes and specs. If you have any suggestions on improvements for the weighting scales, you are invited to leave feedback on this Wowhead forum thread.
One feature the Wowhead weighting system has that is missing in some other systems is intelligent gemming. Most of the time, socket bonuses are not sufficient to make it worth matching color, since one gem is overwhelmingly better than the others for your spec (for instance, Shadow priests almost always will use Runed gems). But there are exceptions. The Wowhead system will automatically put in the gems that result in the highest net rating, taking socket bonuses into account.
To briefly elaborate on the other new features: there is now a search box on any item listing that will quickly search just within displayed results for that listing; filters can now be quickly created by right-clicking any column heading; source columns now show what NPC drops or sells the item you're looking for, and what zone they're in, instead of just saying "Drop" or "Vendor" as it did before; and if you filter for a stat, that stat now gets its own column in the item listing (example).