The argument against (if the postprocessing is significantly after logging the IPs) is that with dynamic IP adresses, it's not clear how the assignment actually was at the time of logging.
With IPv6 and carrier grade NAT, IP addresses are not in and of themselves the full set of information necessary to identify a system. You need the address + port, and only the ISP can map it back to any individual system.
--Quanah -- Quanah Gibson-Mount Platform Architect Zimbra, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration A division of Synacor, Inc