Tried this plugin on two different WordPress blogs. Immediately after activating all pages of the sites began returning error 500 on every request for ever page.
I had backed up .htaccess and was able to recover one site by restoring .htaccess
On the other, higher traffic, site restoring .htaccess didn't fix the issue. There seemed to be some sort of race condition that spawned over 25 long running processes. I was able to recover by renaming index.php in the blog root and manually killing all the rouge processes.