I have run into:
Web server - the standard issue you know of...who is
DNS - Who will be the authorative DNS server for mydomain.com...my AD server or the ISP name server?
DNS - Subdomain of WHOSE authorative domain?
DHCP - My internal clients are registering their DNS names with which server?
AD/Printers - I get my printers to register in the Directory, but I also have whos?
Let me give an example (this was just when 2k arrived
I set up a company "our.example.com", they have an ISDN router that I setup beforehand and its working great. Everyone knows you must have the server connected to a hub (at least) or the install fails (because the network card isn't enabled.) The first AD server installs fine, no errors, DNS is there and running...its not even thinking its a root server, so I add the forwarder and get started on some others which are easy. Clients drop in no sweat as they are DHCP from the AD machine. Beautiful day, only about 6 hours on the servers and the clients are no sweat. Couple more days and the network is done! Someone calls...there is a problem. I drive over...and there is 1000+ clients in the DHCP, more printers than you have ever seen, and DNS records for most of the western world. Now the server complains about the domain being not found, no authorative DNS and being a pain in my bum.
I reinstall as our.company.local, and there are all these questions I never saw on the first install about authorative DNS, active DHCP scope, this time it thinks its a root server. Why didn't this happen before?
The first time the AD server never gave any DNS messages because it bounced out to "example.com" and joined their domain, became a slave to their DNS including caching, and started participating in serving our clients with their DHCP scope. Any DNS info we had went upstream in the dynamic DNS updates. "Example.com" got this stuff appearing and secured their firewall and my install became a child domain without a parent, worked for a while, then stopped and screamed!
I have seen something not as bad when the AD DNS server becomes a child of the ISP (because the ISP is authorative for the domain name before the server is installed.)
The reasons all the books talk of .com is they expect you are starting the whole company from scratch, will host everything yourself, never need any security from the outside world, have unlimited hardware resources...
Use the .local for your private-internal network!