Build version number seems to be JRO03C, rollouts for takju and yakju on maguro devices have been confirmed, no other concrete info yet on any other builds/versions.
Changes? Seems to be pretty much the same as JRN84D, probably with stability fixes, etc. But when comparing with ICS, there are many new features obviously.
OTA update links:
takju 4.1 JRN84D to final 4.1.1 (JRO03C) : Download official ZIP (thanks CocoCopernicus and mbirth!)
takju 4.0.4 IMM76I to final 4.1.1 (JRO03C) : Download official ZIP (thanks a lot lostinbeta!)
Yakju 4.0.4 IMM76I to 4.1.1 final JRO03C: Download official ZIP (Thanks a lot jellymelly)
Instructions on how to flash the update links, are on Efrant's thread here. Note that you need to be on 100% stock to be able to flash the zips. That means, your radio, bootloader, kernel, boot, system, etc should be completely stock. Rooting is fine though, the update should flash fine on rooted devices but you might have to restore root later on.
Update: Search functionality is NOT being removed with this update, as per this quote from The Verge's post:
Update: A Google spokesperson has informed us that the company has not pushed out any changes to search functionality in connection with the Jelly Bean update.