It'd be great if ReSharper was installed as a .pkgdef file in VS2010. Those files are merged at runtime into the registry by VS, that way you don't have to register R# to the registry directly.
The advantages would be a cleaner installation, and above all, the ability to load R# only for the instance I like. I'm currently developping a Visual Studio add-in and I don't want R# to be loaded into the Experimental Instance (devenv.exe /RootSuffix Exp) when debugging the addin, but I still want to be able to write code with ReSharper in the normal instance. With pkgdef, a simple move of the file from the VS program files directory to the local appdata (and a properly configured devenv.pkgdef file) for the normal instance would do the trick.