At the end of the day, a GBG entry only means that the pub is one favoured by CAMRA members in the geographic area and is one of a quota - sometimes pubs with less good ale are used to fill the quota, while in other areas pubs with first class beer and excellent cellar standards are omitted because the quota has been exceeded or even worse, the landlord has fallen out with the local branch.
I would far rather trust the judgement of some of the people on this site - many of whose reviews have proven spot-on when it comes to beer quality - than I would a book which is out of date as soon as it is published and whose totality is questionable.
Yes, I am a CAMRA member, yes, I have written some of GBG's entries, no I won't toe the party line if I think it's wrong.