Yeah, my guild's existed since May of 2005. We've got 30ish accounts, and a bit less than 50 characters--but not all of our players are active, for various reasons. We're small and mostly RP, but some of us do raid (with a sister guild) and run heroics, together when possible.

We're level 16, and that's an accomplishment. We're still working on several "easy" achievements larger guilds can get with less trouble, too.

We can't hit the daily cap most days, and we're looking at going into MoP at less than lvl 25 and seeing several new levels added on top of our already hard-to-climb mountain. It's frustrating when our sister guild hit 25 in a couple months no problem (they aren't too much larger, but have more active members with a ton of alts); it's not a problem for big guilds, especially guilds who aren't choosy about the kinds of people they recruit (and it's led to new forms of drama and jerkishness there as well).

Small guilds, niche/concept guilds, and new guilds are at a severe disadvantage, not just at the start of an expansion, but especially later when people expect a level 25 guild with a bunch of perks and goodies to help them and their alts level. But not all of the guilds that are struggling to level are new, either. Small, friend and family, or concept guilds like mine are not having an easy time either.