I edited a couple of things in my user profile, where I changed the primary group from Registered to Admin and then back to Registered. In the process, I cannot see the Members menu link, next to What's new. Very odd.
I've fixed it now. I have two user groups, both called Registered. Very confusing! I think that was a result of my vBulletin migration. So I just tried ticking the other Registered box and all is ok now. Phew!