While reading this question on webmasters:
I also checked out stachexchange's source code and while indeed the 'description' meta-tag is missing, just to save a few bytes as Jeff noted in his answer to the question, I found it rather strange to see a 'title' meta-tag in there.
This tag essentially duplicates the html 'Title' tag. My research didn't really turn up any reason on why this tag is there, basically just 'wasting' another few bytes.
Why is this tag there? Why bother including it?