Apple's just released a OS X Leopard 10.5.3 update beta to developers, meaning that the patch is at least stable enough for widespread testing. Among the things being fixed are several memory leaks in CoreAnimation and iCal, but the final release won't be available until an estimated April or May.
http://www.appleinsider.com/article...spread_testing_of_mac_os_x_10_5_3_update.html
http://gizmodo.com/373561/mac-os-x-1053-test-builds-seeded-to-developers