CAVEAT: I have not read any except the Pregnancy guide, which I skimmed in the library once.
Just a bit about them I suppose.
A lot of what I read on MN is good, interesting, etc etc. But I have also read utter tosh/advice with NO evidence base whatsoever and on one or two occasions, dangerous information. Now, I am not saying whoever edited these guides wouldn't have weeded the dangerous stuff out, but I can't really see myself buying a guide authored by a load of random people off the internet.
Also, I am assuming as I haven't found any info on this, that the royalties are going to the site's founders? Again, not really something that I am comfortable with seeing as it wasn't written by Justine Roberts et al.
Would be interested in hearing other people's views on this.