Though I certainly can't give an authoritative answer on that matter, I do vaguely remember some complaints being raised in the past on reviews being sent to users list. Also, this list's info page, http://lists.boost.org/mailman/listinfo.cgi/boost-users, seems to suggest that boost-devel is the more appropriate place to submit library reviews: "This list is for discussion of issues related to using these libraries. [...] If your interest is in library submission, development, or review, please subscribe to the Boost developer list."
But as I already said, this response is in no way an authoritative one, so please don't take my word for that!
HTH,
Regards, Gevorg
Gevorg, thanks! It has been some time since I last read the list's description. I'll probably subscribe to the developers list, too, if only for reviewing this library which I consider too important not to be reviewed :-) Regards, Roland