Bartik is the default theme for Drupal 7. To download Bartik, download Drupal 7.
You can find documentation about it here: http://drupal.org/documentation/themes/bartik
A huge thank you to the dozens of people who worked on this theme, and to everyone who supported the effort.
Any bugs found in Bartik should be filed as part of Drupal core. You can read the list of reported issues, or file your own (Project: Drupal core, Componant: Bartik).
If you are having troubles with your own site, we recommend asking for help in IRC or posting a question in the forums. Browse the forums to see if someone else has written about the same problem. Or read documentation. "Issues" (despite the name) are for bugs in the software, not site-specific needs.
The Bartik theme is named after Jean Bartik, one of the original programmers for the ENIAC computer. (Pictured on the left in the photo.)
We are saddened to hear of Jean Bartik's death on March 23, 2011, just two months after Drupal 7 was released. Take some time to learn more about her and the women who invented computer programming.