Due to support issues with a 3rd-party vendor our installation of SQL Server must be changed. In an nutshell we'll be uninstalling R2 and installing R1 clean. Will we be able to get away with a backup/restore or detach/attach solution with regards to the databases? Or will an entire ETL process be required? Has anyone attempted this? I know 2008 -> 2005 won't work, but if both are 2008...
I have really only dealt with editions of the same version, going from Ent to Standard in which I have had no problems. Since R2 is a different version I suspect issues. You would of course want to try this on a test server before doing it in production, but try changing the compatibility of the user databases from R2, then detach and attach them to an R1 version. Run through you tests. If all is well move forward.
you cant restore a backups from higher version of SQL Server, The same applies for attach method also. as William suggest you can use various method to transfer data, By using Redgate tool called SQL Object Level Recovery Native you can restore individual DB objects except Users and Logins from SQL Server 2008 R2 backup to SQL Server 2008 (i am not sure for 2005 and below).
With @Cyborg on this one. There is no way for you to attach, restore, or mirror to a lower edition. If you find a way, you will be way unsupported by Microsoft. Like @ramesh and @Cyborg said, your best bet is to export the data with a 3rd party tool or generating scripts. That is a painful process though. You can always go up, except if you enabled [15,000 partitions support on 2008 SP2]. :