Recently hit 4000, with ~2000 in a single window. One thing that I think helps is remembering that you (ostensibly) have a browser history. Rather than keeping every tab you might want to come back to, close the ones you expect to be unchanged later (or that don't currently hold a particular needed state). You can then reopen ones that float up to your consciousness (i.e., the ones that are important) as necessary. Taking this approach made culling 1000 tabs not too difficult. Of course, this would be made much easier with a robust history search function, but good luck with that.

There is also at least a Chrome extension that lets you filter and close tabs by domain (name escapes me).