Nokia released Nokia N900 PR1.2 today as download from http://tablets-dev.nokia.com/nokia_N900.php and it will be available on over the air update from tomorrow.

If you want to re-flash your device with download Maemo flasher from

http://tablets-dev.nokia.com/maemo-dev-env-downloads.php

Image files

RX-51_2009SE_10.2010.19-1_PR_COMBINED_MR0_ARM.bin

RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin

from http://tablets-dev.nokia.com/nokia_N900.php

Don't forget to read flashing how to at http://wiki.maemo.org/Updating_the_tablet_firmware

There is no info about official change log but see Maemo.org wiki for collection of known changes

Update: See post http://nolovelust.com/post/Nokia-N900-PR12-Officially-Released.aspx for official relese of PR1.2

It took so long but it leaked :)

File name: RX-51_2009SE_10.2010.12-9_PR_COMBINED_MR0_ARM.bin

MD5: 013f4466e5899a9da0c34d5fa6b49b0c

SHA1: 6bb73a3cdcaf34ae5b7a7a4c3cba08b23ea1c058

Apparently it is RC of PR1.2 and was posted to http://talk.maemo.org then got deleted around after 12 hours by administrators due to it being unauthorized distribution.

You are probably looking for download link too but I can't distribute it here. Try usual places  

Please note that according to tweet from nokia conversations it will damage your phone http://twitter.com/nokconv/status/13299314191