Hey, thanks for replying!  I don't remember having crashes really recently, but I have had the game crash from a bad downloaded house relatively recently.  I did end up going to the back up, sigh. I really hope it doesn't happen again, but I definitely will back up more frequently now!

I play on a Intel Mac Mini.  I only have the expansion packs up to Open For Business.  I haven't downloaded any new hacks/mods recently.  I have added custom hair, clothes, furniture, and recolors of Maxis items.  I played my Veronaville University yesterday with no problems.  Today I went into my Veronaville Bluewater Village to look at some recolors of clothing racks and to build a new store.  After I had built the new lot, I looked around and noticed that Chester Gieke and Jodie Larson and her brother were missing.  Their houses were still there, but now up for sale.  I went into my Downtown which was fine and went to a house where Chester Gieke had been visiting.  He wasn't there and my sim had a memory of meeting 'subject'  I use the Insimenator and used the Summon tool and paged through all the families, they all seemed to be there except those two families.  Then I changed neighborhoods and went to my custom neighborhood.  Everybody was missing!  I had no controllable sims (I don't know about townies, since I had no one to play) at all.  I quit the game and looked at the Neighborhood folders.  The amount of characters in my custom neighborhood folder was definitely less than it should have been.  One suggestion in a MATY thread was to delete the Neighborhood controller and let it respawn, so I tried that.  I went back into the game and looked at the University in Strangetown, everybody was there.  I tried Bluewater in Veronaville again, it took much longer than normal to load and when it loaded everybody was gone!  Then I loaded Downtown and everybody except one family was gone. When I visited that family the game seemed to think that I had just installed a new expansion pack!  Then I visited Veronaville and four families were missing.  In University the dormies from a new dorm that I added a few days ago were missing.  Everybody in my custom neighborhood is still missing. 

Please, does anybody have any suggestions?  I'm scared to go back into the game!  I do have a backup, but it's from a couple Sim weeks previous.  I'll back up what's left of my families right now, but is there any way to get them back?  Is this going to keep happening?  In my Characters folder for Veronaville there are now four "TempDBSegmentPackedFile_1197669711.tmp" which weren't there before.  I don't have anything on my computer to run regular Windows programs.