I noticed a performance issue starting this sunday morning with a lot of 504 Error (running WP 3.5.1, plugin Version 0.6.3) on only two of my WordPress sites. The other ones were working perfectly.
Increasing time-out for nginx and php-fpm did not much and the pages were just very very slow to show up. After extensive tests on my server I remembered the last things I have done on these two only sites that caused troubles was to update NewStatPress.
After desactivating NewStatPress in both sites everything went back to normal.
To be sure of this I reactivated the plugin on one site and the performance problem showed up again immediatly.
Everything worked fine previously to this update and my other sites on which I did not update the plugin work fine.
I just think I should let you know.