I took a lot of your valuable reviewer feedback (thank you, see earlier post) and completed my whitepaper entitled, "Developing a Transactional BizTalk Adapter Using the Microsoft Base Adapter Classes". You can download it at http://download.microsoft.com/download/3/7/6/376a6f6c-8c97-4ab5-9d5a-416c76793fbb/Transact_Adapter.doc. The paper discusses at a low-level (with code snipets) transactional adapters, the Base Adapter classes and their hierarchy, and additional rarely-documented adapter design issues. So take a look and pass it on to anyone doing adapter development.
After you read it I am very interested in your feedback - please post here if you would. Hope this helps!