Integration Challenge: BizTalk Functoid Blues

Recently I was facing an integration challenge by creating a custom functiod to use in a mapping. How do I create a custom functiod? Well one can look at a sample on a machine, where a BizTalk instance is present (usually C:\Program Files\Microsoft BizTalk Server 2006\SDK\Samples\XmlTools\CustomFunctoid). Important is to import the BizTalk assembly: Microsoft.BizTalk.BaseFunctoids. This one can