What is the best way to code UDF's for Excel using VSTO in VS 2008?

Are we still using an automation add-in through COM, or have they developed
a slicker way of exposing functions?

I noticed that if I'm using Excel Services (through SharePoint) that they
have a simple attribute that defines a function as an Excel UDF, as follows:
[UdfMethod(IsVolatile = true, ReturnsPersonalInformation = true)]

Is there something like that if you are not using SharePoint?