These are the changes to the CSS Genesis made in version 2.0. The XHTML selectors are listed on the left and the new HTML5 selectors are listed on the right.

genesis-HTML5.css

/* Structural
--------------------------------------------- */
#wrap                  .site-container
#inner                 .site-inner
#content-sidebar-wrap  .content-sidebar-wrap
#content               .content
 
/* Header
--------------------------------------------- */
#header                .site-header
#title-area            .title-area
#title                 .site-title
#description           .site-description
 
/* Navigation
--------------------------------------------- */
#nav                   .nav-primary
#subnav                .nav-secondary
.navigation            .pagination
 
/* Author box
--------------------------------------------- */
.author-box strong     .author-box-title
.author-box p          .author-box-content
 
/* Entry meta
--------------------------------------------- */
.hentry                .entry
.post-info             .entry-header .entry-meta
.post-meta             .entry-footer .entry-meta
.date                  .entry-time
.author                .entry-author
.post-comments         .entry-comments-link
.categories            .entry-categories
.tags                  .entry-tags
 
/* Comments
--------------------------------------------- */
#comments              .entry-comments
.comment-author cite   .comment-author span
.commentmetadata       .comment-meta
.reply                 .comment-reply
#respond               .comment-respond
 
/* Sidebars
--------------------------------------------- */
#sidebar-alt           .sidebar-secondary
#sidebar               .sidebar-primary
 
/* Footer
--------------------------------------------- */
#footer-widgets        .footer-widgets
#footer                .site-footer
 
/* Search Form
--------------------------------------------- */
.searchform            .search-form
.search-input          .search-form input[type="search"]
.searchsubmit          .search-form input[type="submit"]
.s                     .search-form input[type="search"]