1. you have people entering tags on questions asked : all you need to do is dynamically write the first 3 - 5 tags to the meta keywords and the first 10 or so words to to the meta description.

have a robots.txt file in the root of the web page.

2. the layout
I am pretty good myself with SEO optimized layouts ( and unobtrusive JavaScript ) I could help replicate this exact layout for you to be SEO.

this really is a great system you have...a little SEO will seriously improve the traffic flow.
you just need to ensure : no vulgar / erotic words are being used on this site ( dictionary filtering should sort that out )

also once your traffic flow increases...you do get under-handed competitors...who will try to "hack" your system thats where you need to prevent xss, sql injection ( httputility.HtmlEncode / HtppUtility.HtmlDecode can help a lot there ) and may be introduce a not so blurry captcha. I honestly hate long blurry captchas...

your URLs are pretty optimized :) thats great

I can help with all of the above mentioned if you need me to.