They're an ugly hack, as described their inventor David Butenhof (http://tinyurl.com/butenhof-recursive-mutexes) and aren't supported by all lisps: Allegro, Clozure, CMUCL, SBCL(it has a kind of recursive lock, but it's not a posix recursive lock), so I was thinking of making a 1.0 release in which to remove them altogether.
What do you think ?