There are some bum encampments in the undeveloped areas near the tunnels just south of the Caltrain station, but its not as bad as you make it out to be. That whole area around the station has undergone extensive redevelopement since PacBell Park was built.
The largest tent cities in SF I've ever seen are under the 101 Freeway at Army Street.
Got news for ya, even with Pacbell park the tent cities are still there, and Caltrains still shelling out over 300k a month to clean up after them.