I applied today for an svn account and already have it :) so I just commited my first patch. It's a simple patch to the Picture Frame applet and also some refactorings. I'll sure be commiting more patches to plasma and kde.
I also made a techbase page with all the current known plasmoids. (I still need to add those from playground) you can see the page here: http://techbase.kde.org/index.php?title=Projects/Plasma/Plasmoids