I looked past weekends at the option of building myself some organizational chart control, fully expandable with SilverLight (because it's cool and doesn't take tens of megs of jscripts and html).
I ended up with the version hosted for free on Windows Azure cloudapp (thanks Microsoft).
What it can do?
Zoom in, zoom out, expand, collapse, edit (press enter with a blank password, but the data is not persisted between requests, etc), dynamic edit of WPF-like XAML, etc.
It is very easy to use and customize graphics with some additional classes (from ASP.Net).
It's version is somewhere before RC1 so don't argue if it isn't flawless :).
If someone is really interested in this control as is, give me a sign at contact at sharpdeveldotcom
LATER EDIT: See this post for more informations and sourcecode: