First of all, all the Web2feel themes are able to run on WP3 and above. Please let us know when one of the themes has difficulties with WP3+.
Since the release of WordPress 2.9, themes released by web2feel are using a new feature to enable thumbnails on featured posts and post excerpts etc. Earlier we have been using the Timthumb script from Darrenhoyt.com. This involved creating a customfield and applying the required image url to it.
With the release of WordPress 2.9 we have a new feature called the_post_thumbnail feature. This enables us to add a thumbnail image to any of our post from the post editor itself. Yes, we do not need to use any customfields anymore. We have relied on this feature on Jinsona's new themes like Multichrome, Gamerpress, Pristilo etc.This feature will be used on all new themes from web2feel.com.
It is very very easy to enable thumbnails using this new feature, but since it is a new feature some users are confused how to do this. We have been getting many emails asking how to enable thumbnails on these latest themes. It is explained here http://www.web2feel.com/screencast-on-how-to-add-thumbnails-to-web2feel-themes/
Themes created before Multichromo still make use of the timthumb.php. When configured according to the Setup Guides, they all should work well.