Apple released security update 2008-002 for all versions of OS X. It’s available through software update or as a direct download. The list of fixes is extensive and others who have counted them say they number over 40, I’ll take their word for it.
I installed the update yesterday without a problem on my to Intel Macs running Leopard. A restart is required. I haven’t encountered any problems but with the wide range of fixes there’s probably pieces I haven’t touched yet. There’s three different versions of the update: Leopard, PPC and Universal. There’s three more patches for the same three flavors of OS X server.