Most of them are decidedly harmless. I don't exactly have extended conversations with them, but I treat them like I'd treat any neighbor - say hi, give a nod when seeing them, and if they're interested in chatting, chat a bit.

If you want to help in a non-personal way, St. Joseph's is a great place. (Other homeless shelters: http://www.suntopia.org/venice/ca/homeless_shelters.php).

If you want to get a bit more involved, ping our community affairs people.