In response to players' concern over guild organization and management in Cataclysm, Ghostcrawler's been frequenting a thread answering questions about their design goals for guild leveling and why developers decided to axe guild talent trees.
While you should definitely read all of his responses, there are a few points concerning the new system that really jump out:
- They didn't want to encourage guild-hopping, and forcing a guild to pick and choose among talents would have wound up suiting some players and not others (e.g. a guild leader picking PvE-oriented guild talents and alienating the more PvP-focused players in the guild). Hence the leveling system rather than the almost-inevitable squabble over which talents to get.
- Because only a certain number of people in the guild can advance your "level" at one time, there's a cap on the advantage a large guild would otherwise have held.
- "The guild bonuses used to be talents. They are now more like leveling spells. We call them perks now instead of talents. We haven't cut any content, but just changed the UI from boxes with prereqs to a list."
- The hazing ritual to get into Ghostcrawler's guild "is pretty dehumanizing."