I had the same problem with Safari over the past several months. The toolbar (which includes address bar, google search, buttons, etc) was hidden almost every time I relaunched Safari even though the toolbar is visible before quitting (I manually select show toolbar in the View menu). I tried resetting the default in the customize toolbar option. I trashed the prefs. I even trashed Safari and its library then reinstalled a fresh copy. The toolbar still remained hidden most of the time unless I manually request it to be shown with the "View.." menu item (and then would be hidden on next relaunch).
Now, finally!, I think I found the solution. With the toolbar visible (select show toolbar in View menu), hold the right button over the toolbar area so a contextual menu is shown. Select "Keep visible" in that menu.
Looks like this is a semi-bug in Safari, folks. If the user selects the toolbar to be visible by default using the customize menu, then the toolbar should be kept visible. For some of us, that isn't happening unless we also select the "Keep Visible" in the contextual menu for the toolbar.
EDIT (next day): Sorry for the above. Still having a problem with a disappearing toolbar. Unless I'm missing a hidden button somewhere, looks like this might be a full-blown Safari flaw that affects only some people. Maybe a toolbar-less auto window that popped up in the past permanently changed Safari's internals that users can't alter back again?
If the address bar keep disappearing, then follow this answer: http://apple.stackexchange.com/a/60434/5730
– romaninsh – 2013-02-10T23:04:47.027Is it only the address bar (location) part of the toolbar, or the whole toolbar that disappears? – Arjan – 2010-01-07T21:42:14.287
The whole toolbar that disappears mate – Doz – 2010-01-17T03:18:23.853