My 2 bits with my experience on SEO and my own evaluation of the package.
1. There is no need to be fixated on custom meta description - that is a small advantage. Google manages to put out good "snippets" in the results even without meta description
2. All external links are rel="nofollow". Where did you find one dofollow links?
3. What are the essential SEO boosters which you should incorporate
3.1 There is high possibility that you will have thin content issues with Q&A site owing to following pages
a) tag pages can have only one question (which anyway is a subset of questions page),
b)question page with no answer.
Solution : For pages (Tag, Tags, question page with no answer make it follow, noindex
<META NAME="ROBOTS" CONTENT="NOINDEX, FOLLOW">
3.2 Custom titles for questions page when it runs into multiple pages - Disgruntled Goat has a solution for this
3.3 I am not very certain that rel="next" ; rel="prev" used for questions page is appropriate usage. That's my opinion, glad to hear of others as it is well implemented in the system but I think context is not right.
To overcome this, use Minfy (http://code.google.com/p/minify/)
3.5 Avoid use of categories
3.6 Create custom page with gives list of featured posts which are old, obscure so that google refreshes its index with valuable posts. Keep rotating the content
3.7 Use related posts widget
3.8 If you are using adsense, make sure that it is not displayed on "thin pages" so that you do not get penalized
3.9 This robots.txt is essential
3.10 url canonicalization is implemnted and that is a huge plus
3.11 Mobile : There is some issues there. Site is perfect for Ipads, smartphones but with feature phones it is a disadvantage.
Published mobile markup standards include XHTML Basic 1.1
(http://support.google.com/webmasters/bin/answer.py?hl=en&answer=72462&from=40348&rd=1). However, the use of upper case HTML tage makes it impossible to declare it as XHTML basic DTD in mobile theme.