Without any doubt [`default` attributes are reset each run](http://docs.opscode.com/chef_overview_attributes.html).  I know this not just by trusting the docs, but also because I originally used `normal` attributes and had to manually clean them up at the beginning of each run, which was horrible.  Then I switched to `default` attributes and proved it solved the problem.  BTW, the docs also say "A cookbook should be authored to use default attributes as often as possible".