I always used to be a member of one site (not always the same, but one at a time), but haven't joined any site for a while because at the moment I don't have that much time to enjoy the sites to their full extent.

I have a few memberships for sponsor sites though, but I don't make much use of them except for business purposes. Since I don't have a membership site now, I wouldn't join to see how competitors do it. But if I had one, I certainly would.

There are a few sites on my review site where I'm really curious about how it looks behind the curtain. But I will wait to sign up with them or asking for access to review the sites until my own site has undergone a major rebuild.