Hello and first of all thanks for this great plugin.
I have found a bug in Version 0.2. In WP 3.0.1 after upgrading 0.1.5 to 0.2 all thumbnails from "Image to show" box are missing. Also in WP Smart Image II - Settings there is Warning: Cannot modify header information - headers already sent by (output started at ...\wp-admin\admin-header.php:19) in ...\wp-content\plugins\wp-smart-image-ii\wpsi.php on line 612.
I have found workaround for missing thumbnails. In wpsi.php at line 841 I have changed operator "==" in "=". So "if ( $item == wp_get_attachment_image_src($imagen->ID, 'thumbnail') )" becomes "if ( $item = wp_get_attachment_image_src($imagen->ID, 'thumbnail') )".
This is workaround for missing thumbnails in "Image to show" box, but Warning in Settings remains. Don't know are those two things connected or not.