The Q&A plugin has come a long way since it was first released. It really is a mature product now with a good feature set. I also hear that it is currently undergoing an enhancement so I'm looking forward to what the WPMU DEV development crew comes up with.
I just finished building a new site with it and wanting to open up a new showcase thread for other folks to share their Q&A websites.
Check out my implementation of it at http://teaindustry.net
About the site
The site itself is a subsite on a buddypress multisite network. Registration is handled by BuddyDev's BP Ajax Registration plugin. I also am running the following plugins on the site: Better WordPress External Links, Custom CSS, Dynamic Widgets, Login With Ajax, WordPress SEO and, of course, Q&A!
There are also dozens of core plugins that I run on the network that contribute little things to it.
Theme is Twenty-Twelve with only about 4 custom CSS rules applied to it (mainly to the menu). In addition to the theme styles, I used Q&A's built-in CSS section to add a good handful of rules to give it the look I wanted. The biggest visible change is that I removed the default Q&A menu and moved the post stats to the right. There rest are small CSS tweaks just for polish.
I have pre-seeded the site with about 10 questions from that I pulled out of the niche. I intend to canvas other websites to gather more. I ran a Q&A site when the plugin first came out and found that one of the keys to faster conversation was pre-seeding it with relevant questions. Pre-seeding the site is very important. It also helps to have a connection to the community. Of course, my site is new, I just opened it about 10 minutes ago so there isn't any activity on it.
Currently, in terms of integration with buddypress, as of this post, Q&A is not quite ready for BP multisite, it works in BP, but only the main site. I'm working to get that solved, but I'm only halfway there.
Total build time from start to opening was about 15 hours - thanks WPMU DEV for making such a great plugin!
Anyhow, if you've built out a Q&A site somewhere, share it in this thread and give us the details about what you did to make it special!