I am using latest version of WP Smush.it (v1.6.5) with latest version of Wordpress.
I see the following error when I try to change any WP Smush.it settings under Settings > Media.
Warning: trim() expects parameter 1 to be string, array given in /home/xxxxxxx/public_html/wp-admin/options.php on line 147
Warning: trim() expects parameter 1 to be string, array given in /home/xxxxxxx/public_html/wp-admin/options.php on line 147
Warning: Cannot modify header information - headers already sent by (output started at /home/xxxxxxx/public_html/wp-admin/options.php:147) in /home/xxxxxxx/public_html/wp-includes/pluggable.php on line 876
I see there is already a thread dedicated to this error (http://wordpress.org/support/topic/multiple-warnings-and-errors-using-smushit), but it was marked as "Resolved" without any real resolution of the issue, hence opening a new thread.