[dstillman]

Something's not right there. People use Zotero with libraries with tens of thousands of items all the time. (Some people have hundreds of thousands of items, though that gets dicier.) Not sure exactly what you were seeing, but we'd be happy to debug in the Zotero Forums if you wanted to try again. It's possible to configure a third-party plugin such that it affects performance, for example.

(Disclosure: Zotero dev)