Perhaps it would be prudent at the end of this, the Stack Overflow Decade, to look back into the mists of time to see what was seen by those who came before.
And so, I give you:
A Visual Retrospective
With great thanks to archive.org.
Now, in the time before time, when the great barren chaos ocean of the Internet heaved up HTTP Response 302 - http://www.mozquito.org. stackoverflow.com began the Two Thousand Aughts as a found redirect (capture 2000/03/01).
Then, sometime in 2004 (it appears), the domain went to a speculator and remained for sale until 2008 rolled around and
A Miracle Occurred
A cryptic message and the clock nearly began to tick. (capture 2008/07/03)▼
A couple of months later and pop, the first SO logo and site. Unfortunately, archive.org is missing the CSS and a majority of images from that time. (capture 2008/09/15)▼
We finally get a good shot in 2009. (capture 2009/07/02)▼
Careers appears in 2010. (capture 2010-07-30)▼
February 26, 2011 looks like some network connectivity issues were to be expected. Hiding behind that yellow banner is a Stack Exchange link. (capture 2011-02-26)▼
Hello Stack Exchange, chat, meta and Server Fault. (capture 2011-07-18)▼
Usage of the Community Bulletin: 2012 Community Moderator Election was ending soon. (capture 2012-06-15)▼
In very tangentially referencing Web 2.0 form, careers 2.0 appears later in 2012.
More version = More better. (capture 2012-11-15)▼
First appearance of the site introduction banner along with a sign up link on the menu bar. Chat, meta, about and faq disappear from the menu bar. (capture 2013-06-14)▼
At last: my favorite capture. The stylish, black menu bar and ombre Stack Exchange logo appears. We find tour and help appear in the menu bar as well. However the best aspect is the new Hot Network Questions section where someone on Stack Overflow has asked Why is this private member accessible? - a double entendre which must be seen in context to be believed. (capture 2014-02-15)▼
In early 2015 our split Question/Tags/Users/Badges button section joined the Ask Question button in aligning right. careers 2.0 finally tried to gain some cache by rebranding using the Stack Overflow name.
Edit: And, as mentioned by Armatus in the comments, note the Stack Overflow logo reduction of size and also angle of stack elements - with the highest element going to something like 55° from 80°. As a result of that investigation, I noticed that the sprite sheet for the site changed: old vs new. (capture 2015-02-01)▼
10,000,000 questions! (capture 2015-09-01)▼
Let the notifications commence! The Inbox and Recent Achivements icons arrive in the menu bar (another sprite sheet). (capture 2015-10-14)▼
stack overflow careers departs the menu bar to become a gray Jobs button. The Unanswered button departs. Consider that at this point we're quantifying that Stack Overflow is composed of over 4.7 million programmers. (capture 2016-01-31)▼
The Developer Story + Documentation Beta. (capture 2016-10-31)▼
Beginning in 2016 we were 4.7 million programmers. A year later we have grown to 6.6 million. (capture 2017-02-01)▼
April Fools, 2017. Internet security continues to be a joke. The gray button bar is absorbed into a shaken up menu bar. Stack Exchange is conspicuously missing from the top. (capture 2017-04-01)▼
So in February 2017 we were a community of 6.6 million programmers. By September, someone decided to loosen the definitions a bit and include visiting developers which tops us out at 50 million site users per month. This likely has something to do with courting business directly: "Stack Overflow Business Solutions: Looking to understand, engage, or hire developers?". Learn more why don't you!? DocumentationBeta has gone and Jobs -> Developer Jobs. (capture 2017-09-30)▼
We've captured the second annual Developer's Survey here and entered the modern era. (capture 2018-01-14)▼
Circa the beginning of this question, Stack Overflow Teams peeks it's head out with Slack integration. The top menu is de-cluttered by the addition of a side menu - I think this is configurable as mine is shown as a hamburger menu next to the Stack Overflow logo. (capture 2018-11-27)▼
(and more as I have time)