This section of the handbook contains information specific to Rules 1. The main content of the handbook is still relevant to both versions, however there are some differences between D6 and D7 for site builders and developers. Here you can find many tutorials and examples, and above you can find a manual on Rules.
Rules for Drupal 6 is still up to date and just as mature as it has always been, and this section is still open for editing, so when you have improvements in mind, please make them. However, since there are more users and developers on Drupal 7 (see Rules usage statistics, late Feb 2012), there are more people working on the documentation. You can find out more information about Rules 2 in fago's announcement, It's done: Rules 2 is out!