I was a member for several months. I ended up canceling.
The content was pretty valuable/informative (the periodic interviews and associated materials). I simply found that I wasn't getting much value out of the community forums. And, in fact, the forums were filled with a lot of hot air - people who really hadn't figured out the online marketing game, but were happy to offer their advice nonetheless.
The folks at Copyblogger make great stuff - I recommend listening to their Internet Marketing for Smart People radio show. They get some great guests (Seth Godin, Guy Kawasaki, Steven Pressfield, etc), and Robert Bruce, who hosts, does a great job interviewing.
You'll find some similar good audio content inside the Third Tribe, with some deeper discussions on the nuts/bolts of getting started with a content marketing strategy. But you'll also find a lot of very basic information that, depending on your experience level, may not float your boat.
If what you're looking for is more sophisticated discussions - the kind of higher level of online marketing education you'll get here at SEOmoz - I think Third Tribe is more geared for beginners on the whole.
