I know that a few years back, one had to write Excel Macros in VBA.
You could write COM Add-ins using C# or any language you liked, but
not plain old workbook macros and functions.

It was said that we'd be able to "build Office solutions" using
C# or VB .NET with Office 2003. Did that happen?

And what can be done with .NET code in Office 2003? For example, can
you build custom Excel formula functions in .NET using Visual Studio
Tools for Office, or do you still need to take the Add-In approach if
you want to do that?

If so, when will we have the same freedom to write macros in Excel
with C# that we now have with the soon to be obsolete VBA?