Now, the folks at Gizmodo have found out a way to test this new look out for yourself. However, before you try it, you need to be aware of the following:
To get this trick to work, you must use the international version of Google Search, available at google.com. If you're redirected to a localized version of the search, try this address: google.com/ncr.
Furthermore, you may not be able to reverse the changes to your Google interface without erasing a specific cookie; if you're not comfortable messing with individual cookies in your web browser, don't try it out.
If you still want to do it, the procedure is very simple. Go to google.com, erase everything from your address bar (even the http://google.com) and paste the following code into the address bar.
javascript:void(document.cookie="PREF=ID=20b6e4c2f44943bb:U=4bf292d46faad806:TM=1249677602:LM=1257919388:S=odm0Ys-53ZueXfZG;path=/; domain=.google.com");
Hit enter, refresh (if you're again redirected to a localized version of Google, click "go to Google.com" or go to google.com/ncr once again). Conduct a search, and enjoy your new sidebar on the left!
If you want to revert to the original Google Search, you need to delete a cookie for Google.com, named PREF and starting with "ID=20b6e4c2f44943bb". In the screenshot below, taken in Chrome, the cookie you need to remove is highlighted.