The interesting stuff is that by using the Metacello packaging system one is able to load packages that are compatible with Pharo. Try the examples in the provided intro workspaces of RC2 and check out Dales blog for more metacello news.
After playing a little bit with it and cleaning up my projects I'am now able to load a Seaside sample application - here MetaSource with dependencies like FFI, Seaside 3.0, JQueryWidgetBox, ... just by providing a metacello configuration and evaluating a simple script:
((Smalltalk at: #ConfigurationOfMetaSource) project version: '1.0-alpha1') load
There is also a loader in preparation to ease this a little bit more. However - it is really easy now to build custom images like the one with MetaSource - a simple seaside application: