This is my experience:
I'm the guild leader of a guild called "Team GameFAQs" [GFAQ] and we have 100 members. The common bond that holds us together is the fact that we all post on the
www.gamefaqs.com message boards. In fact, that is the pre-requisite for joining the guild.
As a result, the guild never recruits inside the game...all recruitment comes from the GameFAQs message board. About 85% of our members have been active in the past week with 3 week inactives booted to make room for new members, it all works out well.
The great thing about the guild is the size and mixture. There is a group of new players still going through the PvE and asking lots of questions and that's cool. There's also a group of about 20 ascended who have finished or are just about to finish the game and will start guild battling this week. It doesn't matter where you're coming from, the guild has a place for you.
I think something that helps a guild is organisation. My guild has a Teamspeak server with 20 slots (I pay for this) as well as a messageboard where we can post topics and issues. The guild strives to maintain a mature image and so rude players, immature players etc are removed from the guild (this hasn't happened very often). Having a Guild Hall also gives us a great place to meet and trade/giveaway items. Reputation and being able to maintain an enjoyable and co-operative playing environment are extremely important factors. We're not looking to be the uber-guild from hell but we need to have good standards of behaviour for the benefit of all.
In the end, I feel sorry for the small 2-8 member guilds that are trying to expand. Unless you have an outside way of doing it, I think it will be very hard ingame. Those people crying out for members in Ascalon City are likely to see no success. Organisation is the key.....people need to know you're serious about forming and maintaining a guild rather than hoping people will join and it will become big. This never happens.
In fact, if anyone here in a small guild is willing to give it up to join a well-organised 100 member guild, you are more than welcome (as long as you have a GameFAQs posting account). Our guild messageboard has information for you at:
www.super-robots.com/boards
Sorry, I didn't mean for this to be a recruitment session, just if anyone was interested....
My 2 cents worth about the whole guild thing, anyway.