I have this experience, about Fatal Error Allowed memory size bytes exhausted WordPress after installed a plugin in my webhost. This method I have done fixed the issue.
What you can do and how to fix you have Wordpress 3.1 fatal error upgrade 2011, updating process is failed.
My own story with wordpress 3.1 glitch, Admin WordPress 3.1 Slow Problem which only apply in my admin page.
I suggest you checking your webmaster tools account frequently, this is a step by step tutorial how to fix 404 not found webmaster tools error by adding 301 redirect htaccess, permanent redirect in wordpress blog.
For w3 total cache users, if you have duplicated content notification in Google webmaster tool, read this W3 total cache slash url problem fix.
My experience that i want to share if you have this missing a temporary folder error while uploading image or picture has failed to upload due to an error on your wordpress blog and how i fix this problem.
Merry Christmas!- If you ever get “wordpress internal server error” message in your wp-admin or front end blog, see this post how to fix wordpress internal server error message.
Two solutions and the best way if you are locked out of wordpress.
Fixing the problem if you cant access wp-admin wordpress.
If you ever encounter 404 page error, wordpress not found, read this experience.