If you are in the rough place of having to engage with Microsoft SharePoint on a Mac, you're hopefully at least using Microsoft Document Connection (MDC). While this is still much improved over checking documents in and out from the browser, the experience isn't flawless, and I've had cases where after saving and closing an Office document, I get some error message that my file wasn't saved back to the server. When this occurs, I have wanted to hunt down where MDC is caching files to hopefully recover manually. Quick Google searches yielded no results, but found this through Activity Monitor. MDC caches files at:
~/Library/Application\ Support/Microsoft/Office/14.0/Document\ Connection/Document\ Connection.mdccache/sharePointHostName/subDirectory/fileName
Hopefully this can help with your recovery efforts!