MetalPrincess! I just spent 20 minutes looking for this thread! I remembered that I owed someone a response but couldn't remember the title of the thread or where it was... I need to learn to bookmark these things!
Anyway.... I love it with the Raspberry also! And I add it to all different coffee flavors - but very lightly. I like to add a touch to Toffee flavors. I think my favorite use for Vanilla Custard is to help the Chocolates. I love chocolate but none of the flavorings really capture the full character in my opinion. At this point in time I am happiest with Capella Double Chocolate with some Vanilla Custard added.
I find it is very useful when any flavor is a bit too sharp or artificial tasting. Several of the fruit flavors seem that way to me - most notably Banana and Strawberry. I will mix up the base fruit flavor to the intensity I'm looking for and then add Vanilla Custard to the point just BEFORE it can really be easily identified.