Critical. (Note that documentation can be electronic,
not necessarily paper.) 
QA practices should be documented such 
that they are repeatable. Specifications,
designs, business rules, inspection reports,
configurations, code  changes, test plans,
test cases, bug reports, user manuals, etc.
should all be documented. There should ideally
be a system for easily finding and obtaining
documents and determining what documentation
will have a particular piece of information. 
Change management for documentation should
be used if possible.