BizTalk Adapter whitepaper
Mike McKeown has a great blog where he elaborates on BizTalk Adapter development. He has some nice tutorials, howto’s and whitepapers listed on his blog. Some time ago he released a BizTalk Adapter developent whitepaper regarding transactional adapters and adapter base classes. You should definetely read this if you’re involved in developing new adapters. Also don’t forget to read his other material.