Google PTR?

I'm sure I'm bringing up a topic that's been brought up before, but I figured I'd have a go. Anyone from Google around that could answer to why there is no reverse DNS/PTR with most Google IP addresses (from traceroute, etc)? Alternatively, is there a server that can be utilized by the net operators community to at least get an answer on some of the IPs? It's very frustrating to contend with no PTR records in traces for troubleshooting and the like. Any information (off list or on) would be greatly appreciated. Thanks, Blair Trosper Updraft Networks & North Texas GigaPOP