I’m currently preparing for the SharePoint Application developer certification from Microsoft, TS70-573. During my studies I came across the SPPersistedObject class that you can inherit from if you want to save serialized object data in the configuration database. Generally I think this is a bad idea, but there might be some useful purposes, Charlie Holland mentions timerjobs as one example. Personally I have never had the chance to use SPPersistedObject, but now I know about it I might find a use for it someday.
Charlie Holland has a very nice article on the topic that covers pretty much everything you might wanna know to get started, it can be found here: http://www.chaholl.com/archive/2011/01/30/the-skinny-on-sppersistedobject-and-the-hierarchical-object-store-in.aspx