On the Media Library screen
Notice: Array to string conversion in .../plugins/hammy/WPThumb/wpthumb.php on line 579
Not entirely sure what it's trying to do by casting the $args array as a string and looking for '=' but I guess it's trying to see if people pass in a string rather than an array, in which case it should probably be using array_map rather than casting it. I'm probably wrong though ;)
Same warning when you have a thumbnail already uploaded on the edit post screen.
Nothing major but would be nice to get this fixed up in the next release, Noel. (Then again it doesn't seem to be your plugin directly causing the issue, rather the WPThumb include you're using...)