My initial reaction was to immediately opt out. As you may know I opt out of SE caching and all sorts of other SE 'helpful enhancements'. However, that 4-times (300%) more likely to click... that could be a game changer. So I ran some sites with and some sites without Instant Previews for 100 days.
When someone clicks on the magnifying glass on any result, a zoomed-out snapshot of the underlying page appears to the right of the results. Orange highlights indicate where highly relevant content on the page is, and text call outs show search terms in context.
Many pages have their previews generated as part of our regular crawl process. Occasionally, we will generate screenshots on the fly when a user needs it, and in these situations we will retrieve information from web pages using a new "Google Web Preview" user-agent.
Instant Previews does not change our search algorithm or ranking in any way. It's the same results, in the same order. There is also no change to how clicks are tracked. If a user clicks on the title of a result and visits your site, it will count as a normal click, regardless of whether the result was previewed. Previewing a result, however, doesn't count as a click by itself.
Currently, adding the nosnippet meta tag to your pages will cause them to not show a text snippet in our results. Since Instant Previews serves a similar purpose to snippets, pages with the nosnippet tag will also not show previews.
...in our studies, results which were previewed were more than four times as likely to be clicked on.
First thing I noticed: for the Instant Preview to show I had to allow Google Web Preview user-agent to crawl (yes, I discriminate between bots including G-bots). Perhaps because of the NOARCHIVE policy it came a lot.
Second thing I noticed was a significant increase in G mucking with my carefully optimised targeted titles and descriptions.
Third thing I noticed was NO statistically significant change in query traffic due to Instant Preview compared to sites without. Actually some pages may have lost traffic due to associated Google title/description changes.
Given (1) the statement that opting out of Instant Preview does not affect ranking, (2) that I detest Google's snippet usage, (3) that I see no point in allowing non-value added bot access, and (4) that I saw no value difference, i.e. traffic quantity or quality, between sites with and without Instant Preview I am now totally opted out.
Am quite interested to hear if anyone else has run similar tests or noticed benefits or problems with Instant Previews.
<<<corrected NOINDEX to NOARCHIVE >>>>
Edited by iamlost, 16 March 2011 - 10:11 AM.