In order to see all the current ads, first select the city that you wish to browse, then select the catagory. If you click search at this point you will see any ads that have pictures in that catagory. You can refine and tweak your search by entering price ranges and search terms such as "Honda" or "Bekeley" you can also choose to view ads that dont have images as well, this way you dont risk missing any ads and you can still view the pictures in ads that have them.

Can someone search for items in a certain sub-location such as the East Bay?

Currently the only way to do this is to enter the location into the search text box. This should be changed though in the near future.