UPDATE (25 Dec 2010):
Anyone else want to discuss some idea or contribute with another one?. Maybe this is the wrong date to ask for it. We certainly can wait a few days but the time to finish the Public BETA is coming closer.
Until now there hasn't been any further discussion on the ideas drawn from the chat session. Therefore, I think it is time to begin such a discussion.
I will take the nine ideas I could catch from the transcript (although, I think everyone is open to new ones).
Seed questions. Apparently, seeding questions 'to fill the site' is frowned upon, however, a milder form of seeding can be quite interesting and useful. For example, take a problem you know the answer of, but ask for a cleverer solution. That can be potentially challenging.
Simple questions vs Hard questions. Well, frankly I don't see a conflict here. The site can maintain both easy and difficult questions. Hopefully experts will be attracted to the hard questions and novices can contribute to answer simple questions adding value to the site while, if they're interested, learning from some hard questions. However, let me be precise; obviously, hard questions for its own sake do not attract experts (or anyone, really), as the interest from people is based on particular topics or on certain kind of ideas. Therefore, we need simple and hard engaging questions.
The important thing is questions that can be answered in a high-quality way. It is a safe bet to assume we all agree on that. However, one question could be 'How can we assure that?'. As far as I know, the only way to manage the quality of the answers is by managing the quality of the questions. Of course, it would be great to hear other ideas.
Posters for promotion. That's a wonderful initiative. I think that the initial idea is to get those posters in universities, which is perfectly fine. Besides that, it could be very helpful trying to distribute them online. Where? As already was mentioned in the chat session, getting relevant blogs to mention the site is a great idea. Using a poster could be a less awkward way to promote the site for the blogger and a smoother way in social media.
Get promotion by getting relevant blogs and other sites to mention the site. I think I covered that part in the last point, so I leave it there.
Using the Stack Exchange team to get support. As this is very generic, it would be very nice to come up with particular ideas. For example, I mentioned to David that I found a bit worrisome to notice that the site doesn't appear in a decent ranking for general Google searches (such as 'Physics forum, Physics Q&A, etc), even if some of the questions do appear when a search is very specific. I think this is one of the things in which the Stack Exchange team can be quite helpful.
Improve the titles of the better questions in the site. Well, I doubt very much that that can result in an appreciable boost in the site popularity. Nonetheless, it can be good in the long run.
Asking elementary questions that require expert answers. Maybe someone else will chime in to offer a possible way to do that.
A great answer could be not recognized as such by the asker. I think that answers need to be targeted to the appropriate level of the asker, minimizing the possibility of having the OP unsatisfied, except when the quality of the question is not acceptable.