Has any progress been made on the Sphinx module to make it compatible with Windows? How much work needs to be done to allow it to work in both Linux/Unix and Windows environments?
Can't say I have used Sphinx on windows (plenty of unix deploys though). Hamish (man behind the sphinx module) has actually changed to working on a fulltextsearchable module which one of the goals is windows support. Still in the very early stages however - https://github.com/silverstripe-labs/silverstripe-fulltextsearch. You may also want to checkout Marcus's Solr implementation as that also been known to work well on windows.
Have you tried sphinx on windows yet? Do you get any errors? From what I can see people have got it to work so not sure what related to the module might need to be tested (tmp dirs for one!)
I haven't attempted it, yet. I may give it a shot sometime today. If I get it working on Windows, I'll update this thread with my modifications.