Two or three years ago there was quite a bit of interest in public calendar marketing. Those were the days of meetup.com and eventful.com. I think Apple might have tried something with their now defunct .Mac service (anyone remember Apple's original pre-AOL service?!), and in June of 2007 I signed up with Google Public Calendars to market inline skating events in the twin cities.
The services never took off, though both eventful and meetup are still around. These days Facebook looks like it will own this space -- albeit with severe data lock and proprietary transactions.
I suspect calendar search and sharing will return in a few years, but it's not surprising that Google has quietly  ended their calendar search project. This is from a Help entry (some emphases mine)...
We've decided to discontinue public calendar search and the public calendar gallery. These were specialized U.S. English-only features that weren't used as extensively as we would have liked, and proved difficult to maintain over time. We're looking at ways to make it easier to search and browse public calendars, but for now we've removed the gallery and public calendar search function.
Here's what's not changing:
- Public calendars are sticking around.
- You can still create public calendars, and there are a number of ways to spread the word about public calendars you create or you subscribe to.
- You can still add a public calendar to your list of calendars.
- If you have public calendars in your list of calendars, they'll stay there.
- We'll still list the most sought-after public calendars on a static page, just as we've been doing in other Calendar languages. You can access these calendars by clicking the Add down-arrow button (at the bottom of the calendar list on the left) and selecting Add a public calendar.
- Calendar search is sticking around.
- You'll still be able to search the contents of any of the calendars on your list -- including any public calendars you add.
I don't mind Google's ending the marketing of public calendars. It clearly didn't work. I will be really annoyed if they end public calendar support altogether, but I think we're ok there.
Interesting to note the language aspect. They really don't want to be english-centric.
 I follow their blogs and I sure don't remember any announcement. I only learned of this via another post, I don't know when they terminated the service. Really, this should get an "It Died" blog post.