I've been delighted to look in very early in the private beta and see lots of questions. However, I'm a little concerned about the nature of these questions.
The majority seem to be at a "popular science" level. They are interesting to me, because most of them are not in my field, and I'm sure they'd be of interest to people finding a geoscience site on Google to answer those queries - but I'm not sure that they are what is going to attract experts to take up residence here.
From the guidelines that we click through to ask a question on here,
Stick to actual, real, objective questions with concrete answers that a working professional or expert in this field might encounter as a part of their actual, real, job. Stock the site with a bunch of on-topic, expert questions and answers, so that when the site opens to the public, it’s already pre-populated with a bunch of the kind of content that will attract other experts.
The important point is that our objective at this stage, AIUI, isn't so much to attract lots of people who are casually interested in the answers to things like "Why is the Earth not a sphere?" or "Why is the inside of the Earth hot?" (not singling those out for any particular reason, there are lots of examples). We want to attract people who know the answers to those, but who want to ask detailed questions that are relevant for their jobs - because they are the experts who, if they stick around, will allow the site to grow and provide great answers to all levels of question. Those people may, I fear, be put off if they see a popular science site rather than one that is useful to them professionally.
-Simon (NB just my 2p, I have no standing with SE or this site, and no past experience with SE private betas. And no, I haven't asked anything yet... blush)
EDIT: This question, and the discussion following it, on meta.astronomy, sums up my concern better than I can :-)