Marty Waz announced a new tool that will save time and effort when deploying those assemblies that somehow got missed or dropped when replicating between machines. This tool, the BizTalk Assembly Checker, will compare the assemblies that are registered in the BizTalk configuration database with the GACs of each machine in the BizTalk server farm and will notify you if any of the assemblies have not been GAC'd. You can choose to use this tool to copy the assemblies and register them. This is a great tool and I second the recommendation.
Read Marty's post about the BizTalk Assembly Checker, and then download the tool.