I didn't notice it either. I'm on a 27" iMac though. I'm sure if I was on my Air it might be different.
I'm on a 30" monitor and noticed it right away. It's pretty annoying.
I noticed because I wanted to click to the front page (coderwall.com), but when I scrolled back to the top, the banner was covering the 'coderwall' logo/link/branding. Had their been a button to close it, it would have been preferable.