Starting with release 7.0.1 Lotus Domino is supported on 64-bit versions of Windows, Linux, Solaris, AIX, and i5/OS. 64-bit enables the Lotus Domino server to address memory above 2 GB.
The current Lotus Domino server is still 32-bit based. A 64-bit version of the Lotus Domino server will enter beta testing at the same time that Hannover and Domino Next ship.
[Via dominoblog.com]
For more information on Domino and 64-bit please see the article called “The 64-bit question?” on the Lotus Notes & Domino pages and the FAQ on the Lotus Domino support pages.