Here's how Sharepoint Themes should be implemented, check out these impressive themes by Infotech Canada.
Having tried them on our WSS sites I was amazed at how these themes liven up the original dull looking Sharepoint sites. The subtle changes such as the tabbed effect menu bar and the thin web part borders makes a big difference to the look and feel of the Sharepoint site. In my opinion these themes are better than the ones that came with the official Microsoft Sharepoint application templates which were released a while ago, these older application templates are demoed on Bil Simer's Sharepoint site.