I was a D23 Charter Member and always will be. I have not renewed my membership, however. There are several reasons for this, but it mostly boils down to a simple lack of what's in it for me.
The best thing, by far, is the quarterly subscription to the D23 magazine that comes with a membership. The magazine is gorgeous and full of useful and interesting information, but it isn't something that I have to own. It's not the type of magazine I want to keep as a piece of memorabilia, and I can get all of the information out of it that I'll ever need by flipping through it at the bookstore. While it is a wonderful magazine, it really isn't worth purchasing.
Another huge feature of being a D23 member is having access to a ton of "special events" all about Disney. Well, these events might be nice, but, living in Golden, Colorado, I wouldn't know. I make it to California once a year for my annual trip to Disneyland, but that's it. If you don't live near Anaheim or New York, there are virtually no D23 events open to you, unless you are willing to pay 2 memberships' worth for a plane ticket.
Now, I will concede that the D23 Expo is a special special event, but it's still not worth the membership+plane tickets+a hotel room. The expo might be that great in 5-10 years, but they're still working out the kinks. The expo will constantly improve, and I'd be a fool to go this early (although there are some really great seminars and things...but it's just too much money).
The one thing that had me on the fence were the nice little pieces of Disney memorabilia that D23 sent out. Not because they had to, but because they wanted to. I loved getting them--the Matterhorn patch, the Christmas card reprint, etc. Those were great, but I figured I could pick one up on eBay if they sent out something really great. Nevertheless, it really was a nice touch that made being a part of D23 a bit more special and exclusive.
So, I am no longer a member of D23. If I move to California and become closer to these events they offer, or if they make the magazine twice as long, I'll consider rejoining the ranks of D23, but, for now, I'm staying out of it.