A fantastic tool that ships with BizTalk Server 2006 allows you to step through an orchestration which either completed or was suspended for some reason. This is very useful for forensic analysis aftern an orchestration fired, as well as for debugging a problem.
The beauty of this debugger, of course, is the visual aspect of the debugger. Moving down the call stack, each BTS shape and expression is highlighted to indicate entry and exit of the shape. Not only is this the future of debugging, but this is the future of programming as we know it.