Since BizTalk 2002 was not integrated with Visual Studio it was up to each developer to remember to manually check out/check in each of the BizTalk artifacts. This was problematic since most developers were focused on getting the work done and before they new it the day was gone. It was not uncommon at most clients that I worked with for them to be days behind on their check-in's.
Now that BizTalk 2004 is integrated with Visual Studio it is easier to integrate BizTalk with Visual Source Safe. And, for the first time BizTalk projects and non BizTalk projects can be seamlessly integrated with automated build systems such as NANT (Scott Colestock has a great write-up on this).
There are, however, some issues with this integration. The issues center around how Visual Source Safe handles Unicode files. BizTalk creates the schemas, maps and pipelines using UTF16 encoding. To get Visual Source Safe to properly handle these files, use the Visual Source Safe Administrator to change the *.XSD, *.BTM and *.BTP files to binary. This will ensure that Visual Source Safe will not try to change the format of these files.