After a successful update and full scan, the Main Page shows the current date of the successful scan. However, the next day I get the message that a scan is recommended and indicates the last scan was 8/26/2009, almost a month earlier. Any suggestions as to why this is?

It doesn't affect all users all the time - sometimes, like me, it happens once and never again. According to Lavasoft, the last scan date bug has been fixed in the upcoming update. It has to do with the Ad-Aware Service not shutting down properly, so the last scan data is not written properly.