I complain about Google, Bing and other companies a lot here. But it has been a while since I offered some suggestions.
This morning I tweeted that I would expect to see a new feature in Google Webmaster Tools to manage the new Page Previews in the Google results. I base these suggestions off of seeing a lot of questions, concerns and complaints in the forums.
Suggestions for Instant Previews in Google Webmaster Tools:
(1) Re-Fetch Preview Request: A way to request new screen shots of your page previews. Honestly, it really doesn't have to work, just a placebo thing, like we have with elevator close door buttons and walk light buttons.
(2) Remove Preview: A way to tell Google you don't want your page preview to show up via Google Webmaster Tools. Yes, you can do this via the nosnippet tag, but why not add it in Webmaster Tools like you have for removing Sitelinks.
(3) Preview Impressions: Show in the stats section, how many people see your Instant Preview. You can plot it against the impressions and clicks, to see if people are looking at your page preview but not clicking.
Those are my ideas. I also posted them in the forum.
Forum discussion at Google Webmaster Help.