<p>What internal web service did your company implement first? What did you learn?</p>

Let me see if I can get this conversation going. My company implemented a wrapper around the most common Active Directory look-up needs. I imagine this might be one of the most common things to do first in Microsoft/.NET shops.
Anybody implement a library of utility services? Write a facade to some SAP module? Wrap up some services for Human Resources? I'm curious to what people are working on.