I have made this point before so I hope you will forgive me from making it again.

I think the main thing that is holding back better use of Boost Build is the fact that it is very difficult, if not impossible, for an end-user of Boost Build to understand how the final command line parameters are generated for a particular rule. In other words, given the plethora of ways in which options for a rule, such as 'compile' or 'link', are specified, whether via a toolset, a project, a rule, or the command line itself ( did I miss anything ? ),  I think it is important for the end-user to understand how he can change things to add, subtract, or replace a given command line option for commands generated from a rule. Clearly merely adding some Boost Build feature to the command line does not always work as one suspects it should. Since the process for generating command lines for rules in a jam file is pretty complicated end-users of Boost Build become completely lost in trying to understand how to change the way Boost Build creates commands, and this means that Boost Build is much less "usable" then it could be.