I'm still in the process of developing a template/theme along the vein of Drupal's Zen theme. I took a break from what I have so far and also used a bit of the process to cook up my first "shared" theme. The idea behind this design was that it could be used for a child-themed website.
I named it DayCaring.
It's pretty simple, not a huge amount of graphics which should lend to a fast load. A good deal of the graphics load went into the header where I used a sort of "parallax-effect" I wanted to experiment with. I used this page for inspiration and to see how it could be done. Because the look of the site is kind of flat/cartoony I didn't bother blurring the layers to reinforce the illusion of depth of field.
Another sort of special effect I wanted to try out was using JQuery to enforce the height of sibling divs. I think it worked out pretty well. This is a design problem that a lot of XHTML/CSS designers run into when creating a tableless layout. How do you make the shorter div with a colored background extend to the length of the page when the column next door is longer? Usually you cheat.
I tested this on Firefox and IE 8 (and 8 in compatability mode) and will probably run it through Safari and maybe IE 6 if I'm feeling particularly masochistic. It seems to work pretty well with all the content in the standard Joomla "sample content" output. I tried where possible to make allowances for WYSIWYG editing, adding images to content, and so forth.
Download the theme here.