I have used buses in SF. They are unreliable. Sometimes a bus just never shows up, regardless of what the schedule says. Then two buses show up at the same time. This has happened to me several times.
This is called bus bunching, here's an explanation. http://www.wbez.org/series/curious-city/why-buses-arrive-bun...
Bus bunching is, as that article notes, kind of inherent to the system.
And the obvious solutions (like leapfrogging) drive people crazy. Actually, a lot of Muni's problems relate to "people get really upset when you do the obvious fix". Like reducing the number of stops... good luck with that!
Just two? You've never caught a bus in Chicago then..