I always have my own guild for my team any my family members... That said, I overheard the people on Faeblight talking about my mbox guild "Legio IX" on the level 50 chat a few weeks ago so it must be a "large and well-known" guild... I'm still playing Rift pretty much every night and enjoying it a lot.

I mostly have my own guild because the guild bank makes it so easy to coordinate gear and items among all my characters.

With "established guild", what do you mean? Highest guild level? Longest raid progression? Most active people? Doing raids with just multiboxers?