So, we now know what the Ethereal Transmogrifier will be up to in (projected) 4.3 - take two items you have and make one look like the other if they're the same base type. For example you'll be able to take your ass-looking BiS Ret Boots and remodel them into a skin that looks much more appealing. So long as neither are Lengendaries that is:
You will not be able to transmogrify using a legendary item as either the source or the recipient of a change.
Though given the no-doubt coming s**t-storm over that it's questionable just how long that particular rule will remain in force.
Anyway, almost everyone and their dog is justifiably going on about making their set look like the Tier 2 for their class. Unless you're a Warlock, in which case you can pretty much choose whatever Tier you want because they're all awesome. However at this stage it looks like you'll probably need to source that item, and that's not all together easy in the case of the early Tiers - drop pools on Molten Core and BWL bosses were *huge*, and they've still got a lock-out preventing you from re-running them multiple times per day. Not all is lost however, in Burning Crusade many of the models were recoloured and re-used in matching item sets which dropped from Dungeons, including most of Tier 2. For example, this snazzy blue recolour of Lightforge:
The whole list of these recolours can be found at Wowpedia.org:
And as a bonus, most of them don't have class specific requirements either. Enjoy your new, or should I say 'retro', look. Just don't use it too much or Blizz's art designers may have a sad.