Orcus,
The PSR2000 is NOT upgradeable from software, as it was advertised. The OS system is on a chip. There are a few minor bugs but nothing that really affects the functionality of the keyboard.
I would most definitely buy from a dealer you trust, such as George Kaye or Dan O'Neil, and be sure you get a keyboard that was produced recently. It will have the latest OS already installed. Also be certain they include the Survival Kit, because it contains a free 2-year parts and labor warranty extension.
$1000 for a used 2000 is not a great deal.
DonM