Brian Harry has recently posted an excellent word document talking about some guidelines to follow when developing custom TFS extensions. The document is definitely worth a read as it gives you a better understanding of the issues behind the guidance. It is quite Version Control API centric and it would be nice to see similar detailed advice regarding the WIT stuff, but some of it (especially the first tip) holds true for all aspects of TFS integration.
I had started ranting about how much I agreed with the document, but I've just deleted the rant as it was getting in-coherent. Just let's say that you should really pay attention to this 3 paged document if you are writing a TFS integration - take it from somebody who found out many of the lessons the hard way :-)
