I just found this out because safari crashed for some reason (with the "crashed after it reopened" message, though I don't remember reopening it). I had 3 tabs open, including one to a reply here on the 'fritter. I went to my history menu, and I found this option to "reopen all windows from last session". I clicked it, and voile!! It reopened all of them, all in tabs, and ALL IN THE SAME LOCATION!!
true, I wish there was a dialog box like Firefox has to resume to trash your previous session when it first starts up after a crash (and it's platform independent), but I heard a lot of people complaining that they forgot to include this feature, but they didn't.
Just in case you didn't know, it's there.