In my case, I had 3.5 running and all other things went smoothly.  There were no errors in the upgrad process and no errors in the logs.  I am assuming this is a mistake in the scripts that the upgrade process is running.  Here is why I believe this.  Once I realized that Google Analytics was not available in my portal I started digging into what went wrong.  It is guite obvious that if something went wrong it either was not logged or did not show up in the upgrade process.  I spent a couple of hours working through all error logs on the server and that DNN creates, there was no errors.  When I started to dig in, I found a post telling me to check if the files where there.  I checked the files where there and available, however, they were not listed in extensions or as a seperate module and they were not part of any interface.  I then verified that there was no reference of any type to the Google Analytics definitions in any table used by the database.  I went through EVERY table and there was absolutely no reference of any type to the Analytics extension.  That only leaves one conclusion, when the upgrade scripts ran they did not install the needed extension file and the extension was never registered with the Database which left no entry to use.  I have updgraded continuously from version 4.7.0 as they were made available so it leads me to believe it is a problem with upgrading the software over multiple core changes.  Now for a solution.  

I couldn't figure out how to create the neccessary extension file to be able to install the module seperatly from my website, even though the files were available, so I downloaded a clean install of the latest version after upgrading my sites to the latest version.  Currently that is version 5.1.2.  Once I installed a clean, brand new installation, I found that Google Analytics was available on the clean install.  I then used the extension control panel to create an installable package.  I installed it on my current websites and it has been working continuously since then.  I figured this should be fairly safe as all that really happens it is adds the needed code to the javascript located on the Default.aspx page so Google Analytics can read the information.  It shouldn't take much to add that in and the files installed but just weren't registered in the database. 

If anyone from the core team would like to comment on whether or not this is a safe idea, I think the community would appreciate it.  This is not just an isolated problem as I have seen multiple posts.  I am going to work on getting the issue reopened in Gemini as it is quite obviously a problem and there is currently no solution.  The issue is closed in Gemini with no indications of a solution and it is supposed to be fixed in one of the earlier 5.X upgrades.  The problem quite clearly isn't fixed and the Analytics module should really be available as a seperate extension addition until the core team does get it fixed.