A few of my favorite tech bloggers have reviewed the question and answer service Quora, and overall it has received high marks. Mark Suster started it off back in August, Robert Scoble, Mahendra Palsule, and Louis Gray chimed in recently. All of these gents have discussed Quora in a positive light. The site features answer voting, tagging of questions, and comments. The service provides a topic follow model in addition to following specific users, and updates participants with configurable emails.
Quora's hot, but not all that novel
One of Quora's strengths and weaknesses is that it's not very different from other Q&A sites. The familiarity is great for giving visitors a warm introduction and easy entry into discussions. But a critical look at Quora reveals it to be structurally similar to existing forums and Q&A sites like StackExchange. Yet instead of a central theme for the site, Quora embraces a broad range of questions, apparently to pursue growth of a wikipedia like knowledge base of high quality answers.
Q&A issues, the half-life of answers
Unless editors continually revisit and update answers, their quality degrades. The nature of question and answer sites is that they're susceptible to time irrelevance even more than similar encyclopedic topics. Both these types of sites require significant upkeep to maintain visitor value.
The topic follow feature is a wonderful way to introduce serendipitous discovery. But unless the category is extremely narrow, following by tag will saturate attention as the service grows. Quality filters to high rated answers helps moderate the flow of content to visitors.
Thus far I haven't participated heavily in the service beyond a few answers and comments, preferring web search, topic Q&A (Stack Overflow), twitter and blogs. I appreciate the time that people donate to answering questions, but I don't see the long term appeal of the site over focused alternatives, or search.