Apple has recently given developers an additional build of Mac OS X 10.5.6 (9G55), which shows no signs of new issues and addresses the few that remain.
Macrumors notes that Apple has begun seeding this build “internally outside of the usual developer circles,” which may reveal it to be the final version before going public. Unconfirmed sources point out that the official release could come as early as Friday, which will be a free update available to all Mac OS X 10.5 users.
Update: 9to5mac’s sources agree with the Friday release date.