At last count, HopStop had two million monthly active users and launched a Waze-like service for reporting real-time delays and other information.
Waze currently provides some data to Apple; after Google acquired that company, this seems like a great move to ensure a bolstering of Apple’s mapping data.
Update: Due to another mapping data acquisition by Apple, I got confused on this one. Hopstop is much more significant to Apple’s future offerings than I first thought; they’re one of very few companies in the world with public transit timetables for many major cities. The only other company that I can think of with that kind of offering is Google.