I've tested Question2Answer during three days, and I like the application very much. But I had to decide to go without Question2Answer, because I was not able to find a suitable responsive theme. In general, it seems that there are not many fully responsive themes available. But, I've bought three responsive themes (most probably the most popular ones). I all cases I was disappointed. The biggest issue was always the front-end usability, which is from my point-of-view essential for a community-based site like a questions & answer portal.