.NET 4.5 is an in place upgrade of .NET 4.0 (Visual Studio 2010). This means that when you install it, it removes .NET 4.0 replacing it with .NET 4.5. This is a departure from previous versions where .NET has been incremental.
I am finding people getting themselves into all sorts of trouble, including running Visual Studio 2012 and Visual Studio 2010 on the same box, or installing exchange 2010 on a server with .NET 4.5 and applications stop working. I don't think a lot of people are aware about this yet, are you?
I know that MSDN says this is supported, if so, how does this work where you have a version that removes the previous version and expect the previous software to work (i.e. .NET 4 WPF applications for example)?
For now, I do not recommend Dev 10 and Dev 11 on the same box, and running .NET 4 applications on a server with .NET 4.5 is asking for problems.
Can sombody shed some light on this, and can you start sending out correct information, as I think a lot of people are finding the upgrade process confusing or destabilising, where clarification on how to approach upgrades and what can or can't be done would negate this issue?