Update Asset Indexes not working for large number of assets
While Craft appears to give you a success message when the Update Asset Index modal displays a pretty checkbox, when working with a large number of assets, if you don't see a loading bar appear or see the indexed assets afterwards, it's possible you are running into a memory issue, and that pretty checkbox is lying.

Likely, if you look at your craft/storage/logs/phperrors.log you will find a memory error. Try increasing the memory available to your Craft install or increasing the memory_limit in your php.ini settings and trying again.