According to the Wall Street Journal, no user data from Google Now will be shared with third parties and though some Now cards will be triggered by location, your location itself won't be shared. If you do tap on that third-party Now card though, it'll launch that particular third-party app and it would get your data as it would normally. So far, third-party integration will only work with Android and only if you have those third-party apps installed. The new feature should start rolling out to Android users some time today.
Source:
http://www.engadget.com/2015/01/30/google-now-apps/?ncid=rss_truncated