Google's users are looking to find information, not looking for a place to contribute it.
Jabbles is certainly right, and listen to blauwbilgorgel too--it's good feedback from typical Google users. When I clicked down randomly, I got to the category "Body Shops in Bowers, Delaware" only to see "No results were found for the search criteria you requested, we have included web search results for your query" with a link to Google's own search results: http://www.explore.to/listing/usa/de/bowers/see/auto/body-sh...
Users dislike landing on pages with no content, and they also dislike landing on search results from Google's search results--especially if it's Google's own search results.
Once you've removed the no-content pages, you still have many issues. I searched for pizza in New York and the #1 result was in Florida. That's poor quality, but even your #1 listing for pizza in New York had no original content. It was just an address, a phone number (which I had to click again to get?), and a map. Everything looked autogenerated. No reviews, images, comments, hours--anything, really.
So my advice to you would be to step back and ask yourself, "What separates explore.to from the thousands of other sites that just grab or license data from Acxiom or other yellow page data providers? Why would anyone searching on Google want to land on my pages instead of other the tens of thousands of other yellow page sites on the web?" Then concentrate on really pushing on the areas where you can add value for users.
I see no brazen violation of the Webmaster Guidelines demanding a penalty. As far as I know, manual penalties (and their cause) get communicated through Google Webmaster Tools.
What I do see is architectural issues.
Is an empty page, that is linked to from the homepage. For listing websites: Don't put up pages for which you have no content.
The search result pages are indexable too. Even though the post claims they have blocked these pages in robots.txt, they aren't:
(Won't link as to not pollute your index).
These pages wreak havoc on your crawl budget.
Then on to the issue of original content:
This isn't content that will ever perform well in search engines. I'd even go so far as to say these results pollute the search results. They are an address and hopefully a tiny copied description. What added value does this have for a visitor? What added value does this have for a search engine to present high up in the results?
Look at how Yelp or LinkedIn got people to enter content on their listing pages. Or even Yahoo, look at all the widgets added to listings, to increase the content size and relevancy.
Conclusion: No (manual) penalty, but bad non-engaging duplicate content listings combined with a poor site architecture that allows zillions of page combinations with meager to no content on them. The issue is confounded by not making sure your site is canonical:
Site architecture and SEO is massively important for the success or failure of these kinds of websites, and both seem quite poorly thought out at a glance.
If the site is young, the initial boost in rankings (honeymoon period), will decay overtime and settle together with your page authority, content quality etc. If you see a decrease in visitors, you could attribute it to this initial popularity, instead of a penalty. Current visitor numbers might reflect your content / site quality a lot better.
Look at how SEOmoz helped Yelp produce a solid strategy: http://www.quora.com/How-do-StackOverflow-and-Yelp-achieve-s...
Google will parse js to find links to index, but don't count on getting credit for any content you put in there.
But from Wikipedia/Yellow_Pages:
The term Yellow Pages is not a registered
name within the United States and is freely used by many
AT&T ... never applied for a trademark on the logo. While
they eventually received a trademark on a different
version of the logo, the version with the three fingers was
not considered by AT&T to be proprietary and they in fact
allowed any telephone directory to use it.
Google will actually refuse to take your money.
At least with the organic stuff, you can modify your site.