So I started on a new Drupal 7 project. Got my First Drupal 7 Theme problem. A small blog site for a less-than-famous cook.. but one who LOVES to share new ideas on what to eat. The moment I changed themes was my first disappointment with Drupal 7...
Even though the Regions were named as they were in the default Bartik theme, None of the block content rendered in the expected places. Yes, I saved the individual blocks... and yes, I saved the Blocks page itself.
The problem, it turns out, is that I needed to CLEAR the CACHE here: /config/development/performance
"Not my fault" of course, 'cause we expect Drupal to clear the theme cache each time we visit the theme page - accordingly: http://drupal.org/node/337176 . In fact, even after choosing and saving the new theme as default, subsequent blocks that were chosen, placed, and saved did not show up in their respective regions.
It sucks... but if what you're looking for isn't showing up as expected, kick Drupal in the head by clearing its local cache.