The 2 biggest complaints about Solar have been it being in "beta" and lack of good docs.. Well its been out of beta and in release for a few months now so that should no longer be a concern. As for docs you can find the new and improved manual here.
The documentation isn't 100% complete but its head and shoulders above some of the automatically generated manual pages the project has had before. They're also looking for interested parties on writing a book (collaboration anyone?) about the framework to help developers get started. You can find out how to get involved in his post.