There's a good post over at Jade's that provides a great example of the frustration end-game WoW players can experience when their guildies don't give it their all. The post comes on the heals of a different thread published on the Alexstrasza forums, which covers similar frustrations, but points the finger of fault at other guilds and players instead of one's own.
Who is to blame when a guild's progression becomes a problem? As for my opinion, I think I make it fairly obvious at both locals. So if you're really interested (and you damn well should be!), read both and find out. =)