Just updated WPP to 2.3.1 and noted that the class of the images in thumbnails is now class="wpp_fi" and not "wpp-thumbnail". In the style.css there is still img.wpp-thumbnail. You should update the style.css file too.
Greate the ajax loading for cached pages!!
A little less great the re-introducing of timthumb: I hate it not only for possible vulnerability, but also for server load (not of the plugin but for malicious bots that will continue submit stupid malware to it).