First off, I would say to any leader on the fence about whether your guild is ready to move up. You're more than likely ready. I may have held my guild back a little too long. We beat it with characters to spare on our heavy hitters. So I would say go for it.
But more important than finishing the raid was that I did it with my guildmates. Some people left our guild because we weren't ready for Heroics at the time. But I hung around and took leadership and a couple of other players with good rosters hung around too. We have no whales, maybe a couple of goldfish lol, but the new players got stronger every day and to see it all come together was great.