There are quite a few questions from users about how to use the tools which come up constantly in Q&A because the tool pages don't adequately describe their use.
For example, users are constantly asking if there is a way to find the source of broken links from the 4xx (Client Error) report. Given that it's pretty pointless to have a list of the errors if you can't find the sources to fix them, it's likely a question almost every user of that reports asks. Shouldn't you mention somewhere on the page that the referral pages are available by downloading the full report CSV? See 3 confused users in one question: http://www.seomoz.org/q/question-about-crawl-diagnostics-4xx-client-error-report
Another example: new users constantly get panicked when they see a large number of canonical URLs listed in their crawl reports. Because the reports don't do a good job of explaining the difference between an error and notice (tiny, vague text saying "interesting facts about your pages we found while crawling") users panic when they see a large number of canonicals listed.
Same issue with Too Many on Page Links.
My purpose here is not to deliver an exhaustive list, it's to point out that the Q&A section is a goldmine of exactly the areas where users are having problems. Putting a process in place to monitor Q&A (and your own help requests) for repeat usability issues would very quickly provide a significant list of on-page documentation that needs to be improved. Fix 'em and your users will be much happier and you'll keep a lot of the clutter out of Q&A in the future.
Making these improvements would involve very little effort. Not talking about coding here, just simple annotations to better explain areas that clearly have problems.
Specific example - the above two issues are actually explained if a user clicks on the links - but the fact they are links is almost unnoticeable. Why not at least add title tags to the links noting that the issue is more fully explained by clicking? I'm sure you guys could come up with lots of other ways, but that would only take 5 minutes to make the page vastly more useful.
Sorry to go on here, but these are such simple ways of improving the documented user experience problems that have existed for well over the nearly year and a half I've been a member. A review of the on-page documentation from a new user's perspective would yield a number of other areas that would benefit from updating/improvement, but fixing the ones people already complain about would be a great start.