I have attempted to install SCSM 2012 unsuccessfully multiple times and learned a few things that I'll share that will hopefully save someone hours of time hunting down solutions for these issues.
The first issue I ran into was during the SCSM Data warehouse management server installation, during this install you will be asked for multiple database names, rather than selecting the default names, I chose to append '2012' to all the database names. The install will fail with 2012 in the database names, I tried this in three separate environments and it failed in all three.
The next issue was the SQL instance name, if you create a new instance besides the default MSSQL and include 'MSSQL' in the name of the new instance, the installation will fail. Tried this in a couple of different environments and always a failed installation.
The last issue is during an upgrade from SCSM 2010 to SCSM 2012, about three quarters of the way through the installation it will attempt to make changes to the SSRS server, if there is a web folder on the site with the name 'Data Sources' the installation will fail. This failure will be a catastrophic failure and require a disaster recovery scenario to rebuild/reinstall. The horrible thing about this issue is that if you have been creating reporting solutions using the SQL Business Intelligence Development Studio, when you publish your projects to the SSRS server I believe it will automatically create the Data Sources Folder. For the upgrade, rename this folder, run the upgrade and the change the name back after it succeeds.