Here's a screenie of the 3D interface..  

Click the pic for the full size shot.  I haven't even explored what all you can do in 3d mode.. although I do know that you can paint directly on the model in diffuse, spec, trans, bump, gloss and reflective modes.

Basically what I use it for is to create my trans maps.  I just load a semi transparent copy of the original mesh's template.  Then I open it via the 3d interface and make my alterations.. it's automagically updated in the 3d interface and vice versa.. if you paint directly onto the model.. in whatever mode you're painting in it'll automatically update whatever maps are included in your obj's mtl file.  It makes creating trans maps a breeze.

This may have been widely known; but, it is a technique that I just learned.  It's for getting nice tight lines in my trans maps.  Once I get my trans mapped all chopped up and looking approximately like i want.. i gaussian blur it to like 2.8 pixels.  Then I go to levels and move the sliders for black and white levels each progressively closer to the center until my edge is nice and tight again.  No jaggedy crap anymore.  Learned that while perusing tute vids on clipping masks.