According to World of Apple, Mac OS 10.5.3 (build 9D25) has been seeded. No new issues have been identified this time around, and twenty-two fixes have been implemented, including:
Various printing issues
An issue with Safari bookmarks and .Mac Mail account has been resolved (I'll believe that when I see it)
Issues with mounted Boot Camp volumes
A crash within the Network Preference Pane
So far, 180 fixes have been implemented for this version of the OS. Apple seeded build 9D10 in March and several in the month of April. As of the release of build 9D12 on April 4th, 110 fixes had been applied, meaning an additional 70 bugs have been squashed between then and now.
No word on when 10.5.3 will be released officially.