Email I wrote to the team I was working with, back in December 2003:

Pilgrims,

Undoubtedly with the new standard desktop having 512MB RAM, some bunny will try for 1GB.

Memory >512MB requires some entries to be placed into SYSTEM.INI.

From Microsoft:
Windows Me and Windows 98 are not designed to handle more than 1 GB of RAM. More than 1 GB can lead to potential system instability.

References:
Computer May Reboot Continuously with More Than 1.5 GB of RAM (304943)
“Out of Memory” Error Messages with Large Amounts of RAM Installed (253912)
System.ini
[VCache]
MinFileCache=51200
MaxFileCache=524000

Error Message: Insufficient Memory to Initialize Windows (184447)
System.ini
[386Enh]
MaxPhysPage=30000

Specifying Amount of RAM Available to Windows Using MaxPhysPage (181862)

And yes, we did see a bunny in the field try it, and the answer was “you were warned, we told you it wasn’t supported”.