, Vaccano wrote

So, I am starting a new project at my work.  It is going to be big.  And it will be maintained and upgraded for at least 10 years to come.

It would be really nice to use the new .net 4.5 stuff for this project.

So, you know the extended support for XP ends in 2014, you know you're app will be supported for 10 years, and you're wondering about .NET 4.5 support for XP? What don't I get here?

Heck, if your project really is big, what are the chances it will be in production before XP is no longer in extended support? It seems to me like you're asking the wrong questions.