Personally, I'm not very fond of the whole minimalistic UI trend. I also generally prefer to have everything that I might use in an instance situation (i.e. everything except portals, mount, pets, and trade skills) on bar, just out of convenience. My current UI isn't exactly ideal (slightly too bottom heavy), but it serves all my needs and my tendency towards a large chat window (half the game is communication, after all). One thing I am particular about is a certain degree of balance and symmetry in my interface, and I do believe I have achieved this aim.
More or less, I've managed to work all my must-haves (And no, I will not drop my Mp3 player addon) into the interface in a relatively organized, albeit large, fashion.
