5.1 MSI Documentation
PDFs contained in the Documentation folder created by the 5.1 MSI are all headed: 'Sitefinity CMS 4.4'
Sigh...
I couldn't find any special notes on the upgrade process other than the most general steps with the porject manager.
However, when I did a file comparison of the web.config and sitefinitywebapp.csproj in my project and the 5.1 blank project, there was a lot of new stuff... so I manually merged all the additions. Fortunately I have a fairly good tool for that, but still a time-consuming process.