The KV-S2046C is a big improvement over the KV-S2045C. Mostly because the glass lasts longer without getting scratched. But also because you don't need the SCSI card and cable.
You need to reboot Windows XP about once every 2 hours if you want to use the KV-S2046C with the USB interface. It stops working; the scanner will scan one page halfway and then hang.
Either don't use the KV-S2046C, or don't use Windows XP.
Updated on Feb 23, 2014
I'm the guy who formerly gave this 3 stars for not working well with Windows XP. I've been using it for over a year with Windows 7 now, with no such reliability problems. There is a problem in that you can't use Canon's excellent Capture Perfect 3 software--this is Canon's fault; if you bought Capture Perfect before Windows 7, you need the new 64-bit version, which Canon will not give you nor let you upgrade to. And you can't use either of Panasonic's previous scanning software (RTIV and some other thing). You have to use Panasonic's newest, worst software, Image Capture Plus, which imposes a stunningly large array of truly idiotic restrictions on the user (e.g., you cannot switch scan settings without purging all previously-scanned documents, which means if you have color images you've got to scan them in separately and then use Acrobat Pro to join them).
But the scanner itself is great. If only there were decent software to use it on Windows 7.