i totally agree with you - i believe the 'MP' is just the clay coming out formed to the shape of the intestines. it may be that there is a cleansing effect . . . but the bulk of the material that comes out looks to be the psyllium + clay stuff that went. in.
i also did the blessed herbs cleanse several months ago -- i fasted before & fasted during the 5 day cleanse as well. i'm not saying it was a bad experience -- but actually i think most of the benefit i received was from the fast.
i saw a post by a doctor (i think i found him on rawguru.com) who said he has performed hundreds of colonoscopies & has never seen MP in a persons intestines. so that made me suspect as well. not that i think doctors know everything .... but if yer looking right into the intestines with a scope you'd have to see something if this build up was so common.
anyway, i don't think i'll do another one . . . i've since switched to a RAW food diet & the extra fiber is plenty to keep me cleaned out.