Examples of legit nmap usage?

["Foust, Adam G." <agfoust () tva gov>]

nmap has the potential of becoming an extremely useful tool for me in my job
(not in the hacker sense, but in the discovery and security sense). I ran it
for a while and built up a picture of our intranet WAN (with the help of a
custom bit of perl and CGI programming), but now I'm being told knock it off
for good based on the high amount of messages that began to accumulate in
our router logs. All of our other $$$ commercial network tools have so far
provided a rather piecemeal view of things, and I would like to continue to
use this excellent nmap tool to augment our picture of things (particularly
having an inventory of TCP services).

Can anyone help me out with a good "business case" for administratively
running nmap in a corporate environment? What would be the impact to routers
and hosts of say automating a weekly scan on a rather large network (I won't
give specifics, but I will say that if I seed nmap with a list of ping-able
IP addresses it requires a couple of days to complete a single sweep)? Is
using nmap in this fashion a dumb idea?

Any good examples of nmap being used for network discovery in any
corporations out there?

Any information you can provide would be of great use. Thanks.