Sometimes a new client project inspires you to think a bit differently than usual.
At first I was gonna do a series of little rings, like a chain, as the sidebar divider, just to break up the linear/square/boxy feel.
Then as I thought about the circular rings/links, I imagined a single wavy line instead -- like alternating halves of the chain links -- only really big and curvy.
Then it was just a matter of creating a large scale grid -- onto which I drew some bezier curves in Photoshop. One curve left, and one curve right, matching the transitions of the alternating radii. (I have some mechanical drawing experience.) Then I repeated those, added a stroke, and sliced out just one perfect set.
Lastly, a bit of layering in Photoshop to get the two different background colors on either side of the wavy stroke, and VoilÃ !
Since you guys use the faux columns repeating background image technique, I just created a new, albeit taller version of the Container background image, with exactly one cycle of the repeating vertical wave (and of course, the white side borders built in).
Here's a link to that BG image so you can see it by itself:http://www.yogamatrika.com/ym/wp-content/themes/matrika/images/container-bg.gif
One other note: Since the Container starts up behind the header, I used a background position adjustment on it to push the start of the BG image down a bit to get the exact part of the curve I wanted at the top of the sidebar.
So, yes, a simple idea -- but one that took a bit of engineering to accomplish.