The current background reminds of sitting in a classroom and being punished by mathematics formulas.
Why was this background chosen?
Do others like it?
This is a temporary background, all beta sites will start with it. They're trying to go with a "sketchy" look and feel.
It is sketchy because the site itself is sketchy -- it will only continue to exist, if the site has focus and audience!
While it's pretty much a given that web apps will make it due to popularity, any given site has to ...
... so, there must be enough good questions and answers, a solid population of users, and a certain amount of traffic.