I’ve tried both of the current options, on the right and left of the page. Neither are ideal since the memex results are put on top, and seeing those are typically secondary to seeing the results that Google returns. I would prefer the memex results on the right side, but underneath everything else that can appear there, such as Google’s rich snippets. There have been times when I go to click on those rich snippet results, but then the memex results pop into the space that the snippets used to be (and I misclick). If the memex results were able to be injected into the page lower down on the right, then that would be ideal.
If this was added I’d want to emphasize the option part you included in your original question. I’d prefer above Google Snippets. 
Yes, making it optional makes total sense.
For me, Google’s snippet loads first, and the memex results take much longer to load. It has happened so many times that I go to click on something in Google’s snippet, and just before I click… the memex results bump Google’s snippet down the page and I click on something I didn’t intend to.
I think it would make sense to also load a placeholder for the results there so that this jumping does not appear.
Placeholder would be nice but, my highest priority request wrt this area is to shrink Memex box in general since it pushes the Google stuff down “below the fold” in many cases (so you can miss it), and shrink Memex box to only fit the results that are found, especially just a very small indicator (“No Memex results”), if there are no hits.
