3. Why can't I search by theme or genre?  If I click on the vehicles tab, and then on any of the other sub-tabs, I get a "0 results" page.  I would really like to look throught the catalogue of items there, just like I can here at Renderosity.

Click the Display Options button on the upper left of the Cornucopia page. It's right under the search box.  Make sure it is set to diplay all objects, not just voucher friendly.

LVS - Where Learning is Fun!  
http://www.lvsonline.com/index.html