Can I check if the C# compiler inlined a method call?

No you can't. Even more, the one who decides on inlining isn't VS compiler that takes you code and converts it into IL, but JIT compiler that takes IL and converts it to machine code. This is because only the JIT compiler knows enough about the processor architecture to decide if putting a method inline is appropriate as it’s a tradeoff between instruction pipelining and cache size.

So even looking in .NET Reflector will not help you.

"You can check System.Reflection.MethodBase.GetCurrentMethod().Name. If the method is inlined, it will return the name of the caller instead."

--Joel Coehoorn

There is a new way to encourage more agressive inlining in .net 4.5 that is described here: http://blogs.microsoft.co.il/blogs/sasha/archive/2012/01/20/aggressive-inlining-in-the-clr-4-5-jit.aspx

Basically it is just a flag to tell the compiler to inline if possible. Unfortunatly, it's not available in the current version of XNA (Game Studio 4.0) but should be available when XNA catches up to VS 2012 this year some time. It is already available if you are somehow running on Mono.

[MethodImpl(MethodImplOptions.AggressiveInlining)] 
public static int LargeMethod(int i, int j)
{ 
    if (i + 14 > j) 
    { 
        return i + j; 
    } 
    else if (j * 12 < i) 
    { 
        return 42 + i - j * 7; 
    } 
    else 
    { 
        return i % 14 - j; 
    } 
}