===See Responses In-line==

"Issues are fixed but then they return. For example, we have this post reporting 0 crawled pages from October 23; on October 24, we still had individuals leaving comments saying that the problem wasn't fixed."

For the sites that experienced this problem the issue should now be resolved. Updates to Webmasters Tools usually takes some time to reach all of the sites that use our tools.
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"We have reports that Google Webmaster Tools are inaccurately displaying keyword positions among other issues."

This type of issue is very often dependent on the specifics of a particular site.
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"In the forums, we have a lot of other reports. One webmaster finds that Google Webmaster Central is showing the title of another website as associated with his site. Hacked? No. Bad coding? No. Google Webmaster Tools? Yes--at least, the evidence in Google Groups and other related reports points to that."

This is another case where it's really specific to the site experiencing the issue...sometimes an improperly shared hosting setup can cause these types of problems.
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"Another forum member says that regardless of what she does, Google gives her the warning that there are "too many URLs for Googlebot" -- even if she uses robots.txt to block off the offending URLs."

Robots.txt changes can sometimes take a while to migrate through our crawling system to Webmaster Tools.
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“..Google now tells you where your 404 errors are coming from. Many people are happy with this tool but others actually think it's inaccurate.”

This feature has been long requested and has proven very useful. Yes the reported not found errors do sometimes take a while to resolve after webmasters get a correction in place. For the limited reports of false positives in the thread you link to, those specific cases would have to be investigated further to determine why these URLs are showing up in the not found errors report. Overall I think webmasters are happy to have this new data for improving their sites.
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For all issues like this and any others you might encounter, I recommend that everyone post these in the our Webmaster Help Groups where we have Googlers and long time members who can separate site specific issues from an issue with the tools themselves (which our team works hard on preventing).

Thanks for caring! I'm glad so many people are using the tools and that people let us know when issues come up.

Jonathan

Wow, thanks Jonathan!

Thanks Jonathan -- very helpful :)

The interesting thing to me is how these visible errors in GWT mirror the multitudinous hidden error in Google's crawling and ranking engines.