I've been wanting to try out VS2011 and .NET 4.5 beta, but the upgrade path is confusing at best. If I understand what I've read, the .NET 4.5 framework overwrites the .NET 4.0 libraries on your local machine, so libraries such as mscorlib.dll and System.dll will be replaced with the 4.5 version - fully backward compatible, but still different.
If I'm developing ASP.NET sites with VS2011, and assuming I don't use any of the new 4.5 features in the code, do you know of any issues I might have by deploying to a web server with only the .NET 4.0 framework? I wouldn't expect any problems since it's the same CLR, but I'd like to know for sure before I do it.
There's always the option of keeping a separate virtual dev machine for 2011/4.5 so that I can develop on 4.5, but go back to my original 4.0 machine to compile and publish, but I'd rather not go that route if I don't have to.