Hi John,
First of all - the Google Webmaster Blog has written about infinite content (although not specifically lazy loading) here. Might be worth checking out.
Second, my question to you would be what is your goal with implementing lazy loading on your site? Is it for the site to load faster for users? For overall user experience?
Here is a thread on Reddit talking about this situation, I think /Twoary explains it well. Here's a quote:
"As far as I have experimented with it, it seems like they can indeed not find scroll-based lazy loading (in webmaster tools). Another possibility is onload lazyloading (first load all the content above the fold, then load the content below the fold after the onload event has fired), I have to experiment more with that.
Right now I avoid lazy loading for SEO for articles and such. The fact is that google only cares about "time to first byte". Maybe soonish they will care about "time until above the fold page is loaded". But they do not penalize for the time it takes for all of the resources to be loaded. Apart from that, google mostly cares about user experience which they measure by actual dwell time of their users.
As for the user experience, lazy loading images doesn't add that much benefit either. The browser downloads images near the top of your page first, so the above the fold content isn't downloaded any faster with lazy load. (Possibly even slower because the browser won't be able to start prefetching lazy loaded images until javascript executes.)
The only benefit I see right now is for reducing bandwidth usage (for your site and for mobile users). However the disadvantage will be that your images probably won't rank as well (even if you use pagination/a sitemap.)
OTOH, lazy loading other heavy content such as videos, iframes and ads may be much more beneficial because those actively make the page more sluggish."