It seems to me that working title for a first anniversary post might be along the lines First Anniversary Question: Why does the world need TCS StackExchange?
Such a question would invite very many, very different answers ... which would be good ... and the voting patterns would be very interesting indeed.
Speaking as an engineer, my BibTeX database has a just-added entry from an article in this month's Mathematical Intelligencer, in which following quote is attributed to Alfréd Rényi (and many other mathematicians too):
Other mathematicians prove what they can, John von Neumann proves what he wants.
This saying can be read equally as a tribute to von Neumann's undoubted genius, and as a tribute to von Neumann's ability to apply that mathematical creativity to any of the (many) great programs and enterprises to which his contributions were seminal (logic, ergodic theory, quantum theory, fluid dynamics, control, game theory, and numerical computation, to name only some of them).
Now in the 21st century, mathematical genius is as scarce as ever, and yet fortunately, the ability to "prove what we want" is becoming ever-more-widely distributed. This is in consequence of the confluence of several factors, among which are the ever-increasing volume of mathematical literature, the ever-improving access and searchability of that literature, and the literature's increasing emphasis upon naturality and universality.
And yet, these gains in mathematical volume, access, naturality, and universality aren't much good without the additional crucial ingredient of community … and here both TCS StackExchange and its sister site Mathoverflow have made a contribution that (to my mind) is absolutely essential and wonderful.
Thus (for me), not the sole contribution of TCS StackExchange to mathematics, but also not the least important, is the sense of community that TCS StackExchange fosters, and the concomitant mathematical confidence that "yes, we can prove what we want", which TCS StackExchange so ably helps distribute among many people (young researchers especially).
Surely, an anniversary question "Why does the world need TCS StackExchange?" would elicit very many answers, which would be quite different from the above and from one-another ... and all of these answers would be fascinating to read.
@article{Author = {Domokos Sx\'{a}z},
Title = {John von Neumann, the Mathematician},
Journal = {Mathematical Intelligencer},
Number = {2}, Pages = {42--51}, Volume = {33},Year = {2011}}