There have been numerous reports in the Google Maps Troubleshooting Group over the past few days of missing locations in Maps. Here’s Sparky description the problem:

I’m an avid user of Google Maps, and have between 50 and 100 saved locations, that auto-complete when I type in the search box, in addition to being able to edit them using the arrow link to the right of the search box. 

As late as last Friday the 7th of November, I was using my saved locations to get directions, etc.  This evening, I clicked a “Map This” link from GMail to add another saved location, and it was the only one present in the list.  I was using Firefox 3 at the time, and have since closed out, and signed back in, both with Firefox 3 and IE 6, but much to my dismay, the only location available is the one that I just clicked on from the e-mail.  My default location is no longer set, and none of the old ones appear, even when using the “Edit Saved Locations” link by the search box. Also, the “Save locations automatically” box is still, and always has been, checked for me. 

Google has acknowledged the problem and promised a fix in an email sent this morning by Maps Guide Mike:

We’re currently fixing a problem that has caused some people to lose
access to their saved locations (addressbook) data. The data should be
accessible again shortly – our sincere apologies for this outage.