I've done a base install of EPi 7.5 and upgraded to the latest version via NuGet
Followed up with an EPi Find install (18.104.22.1685) again via NuGet
Sadly, the site now fails at runtime with the error
The references have "Copy Local" set are there (and verified the files appear in /bin), permissions are OK.
Is there a known issue with this, or am I doing something inherently wrong?
The reason might be an assembly which EPiServer.Find.Optimizations.dll has dependencies on, not the dll itself. You might want to turn on FusionLog (http://www.hanselman.com/blog/BackToBasicsUsingFusionLogViewerToDebugObscureLoaderErrors.aspx) to see which assembly is actually can't be loaded.
Occassionally I've seen assembly redirects are not set to the correct versions of installed assemblies after some nuget installs. Worth checking that the redirects are pointing to the versions of the assemblies that are actually installed, starting with EPiServer.Find.