I didn't mean to imply you could do it everywhere. I was specifically replying to the part about "MUNI" in the parent comment. The geo data for current MUNI positions is public data. So if you are making an SFMUNI specific app, there's no excuse not to use it.
Also, I didn't realize that embark also does routing, which is more than iCommuteSF and Routesy do.
Yes, however Muni's own signs at the stops often make inaccurate predictions. As an occasional Muni rider, I've often waited for a bus or a train only to find that it's not in service. There are also frequent "ghost buses", where the minutes count down to zero but no bus shows up.
In other words, although I'm certain the transit apps could stand to improve, I don't think even Muni has accurate data.
Also, I didn't realize that embark also does routing, which is more than iCommuteSF and Routesy do.