People from stackoverflow have been working closely with google team to help them make the panda algorithm more efficient, so I guess they've learned a lot from the google team.
Thus they may have done very clever friendly URLs to maximize the page rank.
I've seen from time to time very long URLs (can't find where) in stackoverflow, but after a certain "amount" of character there were only numbers, kind of "ok passed this length, SEOs will ignore this so let's put only numbers".
I've done a huge work on my framework to make very friendly URLs, and my website can come up with URLs like:
It's very long and I'm wondering if the previous URL won't be mixed with, say, this one: