Railsway cells The german RailsWay magazine 5.2009 features a 7-page introduction to Rails Cells, with advanced topics like testing, nesting and AJAX-supporting cells.
It's available in printed german.
Railsway apotomo An 8-page article about Apotomo introduces widgets in Rails, shows concepts like event handling with Drag&Drop and composed widgets.
Again, available in printed german in the RailsWay magazine 6.2009.

Github

The official github project page.

Chat

The official IRC channel #cells is at irc.freenode.net - the cells developer team is lurking here for your questions. Don't be shy, just come in and ask. We won't bite.

Mailinglist

If you're planning to work with cells, please join the cells-talk mailinglist! Anyone is welcome.

The traffic is rather low. Nevertheless, we're having philosophic discussions about components.