I just checked, we have over 170 unanswered questions here (including 5 out my 6), is this of concern? The unanswered questions are up to 16 up votes.
I think I am going to stop asking questions and answer some where I can.
The statistics displayed on the Area 51 page for the site give you a sense of the goals for the site.
Answer rate: The answer rate at time of posting is 82%. The recommended target is 90%. It would be great if we get the answer rate up a little higher. So if you or anyone else wants to go through some of the unanswered questions and provide some answers, I think that would be great. In general, the answer rate has hovered between 80 and 84% for most of the site's life. I think this can be attributed to the complexity of many of the questions and the general standard of evidence expected. But hopefully as we get a broader sphere of involved experts, the answer rate will start to increase.
Questions per day: However, feel free to keep asking questions. The other statistic that is arguably the most worrying is our questions per day. It currently sits at 2.9 per day, although it is improving. This is the only statistics that is "in the red". I look forward to when it gets up to 5 per day assuming that the quality can stay reasonable and the answer rate doesn't drop too much.
Users & Visits: Keeping the questions coming increases the content and the users. Both of these stats have been growing reasonably well over the last few months.
Bear in mind that the stat 'goals' on Area 51 are an aggregate rough approximation of where sites in general should be, based on our experience. Each site is going to strike it's own level, they all vary.
Having some unanswered questions, especially questions that are on the more difficult to answer side of the spectrum can be a very good thing. If an expert shows up and there's nothing to answer, you lose an opportunity. I've committed to proposals in the past where I arrived to find that everything I could have answered had been answered, and I didn't have many questions to ask.
The hallmark of a good Q&A site is an answer rate somewhere near 90%, but that's just one metric. The time it takes to get an answer is also very interesting, folks ideally get at least one up voted answer the same day that they ask their question, if not sooner.
On sites where only a few new questions come in each day, folks aren't typically hovering over the new question list. As the community grows and people begin expecting at least a few new questions every hour, they'll tend to check more often, thus questions get answered sooner and stand much less of a chance of going by without a lot of notice.
It's great to check the unanswered question list from time to time, but don't do it with the goal of getting a statistic to move. Answer the ones you know you can answer well, and don't worry if some are left for new experts to find and dive into. This is, after all, something that will naturally adjust itself as new questions are asked in higher frequency.